White Chocolate-Key Lime Mousse

Yield: 8 to 10 servings

Tips: Do you know about Key limes? They are small, roundish, yellowy-green limes, with pale green interiors. While not nearly as attractive visually as their larger Persian cousins (the type most commonly available in US supermarkets), they have a very special tart flavor. Key limes are beginning to be more readily available in many markets, too, and you can ask your produce person to order some. The brand I have found most often is C-Brand Tropicals from Goulds, FL; according to their website (www.tropiquality.com), Key limes are available year round. This recipe uses both lime zest and juice. I have tried to grate the zest from Key limes repeatedly, but I have not had great success with it, so I use 2 Persian limes for zest and Key limes for juice.

This mousse has a number of steps, but the resulting creation is worth the time and effort. The mousse will be a pale yellow color and not too firm, with a beautiful tart taste from the Key lime juice. As the taste is not too sweet, this would likely be more appreciated by adults. The mousse will keep in the refrigerator, tightly covered, for up to 4 days; as time passes, the texture becomes less creamy and more spongy, but the mousse is delicious either way. It is eminently possible to make a pie filling from this mousse--see the variation at the end of the recipe. For the mousse, you'll need 8 to 10 ramekins or small wineglasses, each with about 2/3 cup capacity. I prefer to serve this in clear glass, as opposed to the usual white porcelain of ramekins, as I think it looks better that way. This is light-textured, but quite rich, so it would be best at the end of a not-too-heavy meal.

Ingredients:

For serving:

In medium or large nonreactive metal bowl, place thin slices of butter and sugar. Place over simmering water on low heat (water must not touch bottom of bowl). With large whisk, stir occasionally until butter melts and mixture is combined. Remove from heat. Add lime zest. If butter mixture is too warm to be comfortable to the touch, let cool slightly. Add eggs and yolks; whisk in well. Gradually whisk in lime juice. Scrape bowl bottom and sides thoroughly with rubber spatula. Set aside for a moment.

In small heatproof cup, sprinkle unflavored gelatin over cold water. Set aside. Place fine strainer over medium nonreactive bowl; place whole assembly on pot holder and set aside near stovetop.

Stirring constantly with whisk or large spoon, place bowl of lime-egg mixture over simmering water on low heat. Mixture will thin initially, but after about 8 to 12 minutes will begin to thicken. It is important to stir constantly during this cooking period. When you can see definite traces of whisk or spoon movements in the lime-egg mixture, it is done; remove from heat and dry bowl bottom and sides. Immediately pour hot mixture into strainer, forcing it through. (Note: Traditionally, this lime-egg mixture, called a "curd", is not strained after cooking. Straining will remove most of the lime zest, but will also remove any particles of egg that get overheated and form small white lumps-there are always a few, no matter how careful you are. If you want to keep the zest in the mixture and don't mind a few lumps, merely pour it from the bowl used for cooking into a clean medium nonreactive bowl.)

Place small heatproof cup of gelatin and water into a pan with enough barely simmering water to come no more than halfway up the sides of the cup. With small metal spoon, stir just until gelatin is dissolved. Do not overheat. Remove from heat and hot water; dry cup bottom and sides. Add dissolved gelatin mixture to lime curd and stir in well (lime curd will thin out somewhat--OK). Place bowl of lime curd on a pot holder in refrigerator. Stir occasionally.

Place white chocolate, which MUST be very finely chopped, into small heatproof bowl. In small saucepan, heat 1/4 cup heavy cream (reserve remainder) over low heat until very hot, stirring occasionally. Remove from heat; pour about half of hot cream over chocolate. Allow to stand for a minute or two, then stir or whisk until smooth. Gradually stir in remaining hot cream. Set aside to cool to room temperature. Chill a small bowl and the beater(s) from a hand-held electric mixer for at least 15 minutes during this time.

When white chocolate mixture is still slightly warm, check temperature of lime curd. Bottom of bowl should be room temperature or slightly cooler, but not cold. If too warm, and it probably will be, place bowl of lime curd in in larger, shallower frying pan about half full of very cold water and 8 to 10 ice cubes. Stir lime curd frequently. After about 5 minutes, remove from ice water. Stir for a minute or two, then feel bottom and sides of bowl; if these are above room temperature, replace lime curd bowl in ice-water mixture, and check again after a few minutes. Again, check temperature of bowl bottom and sides after stirring curd for a minute or two. When at room temperature or slightly cooler, remove from ice-water mixture; dry bottom and sides of bowl and set aside at room temperature.

When white chocolate mixture has cooled to room temperature (test a bit on the inside of your wrist), beat remaining 3/4 cup heavy cream in chilled bowl with chilled beater(s) at high speed only until definite traces of the beaters show in the cream. All at once, add cooled white chocolate mixture (if it is warm, it will deflate the cream). Beat at low speed for a few seconds to incorporate white chocolate mixture, then beat at high speed JUST to soft peak stage. Do not overbeat or mixture will become grainy.

Add whipped white chocolate mixture to lime curd. Immediately fold in gently but thoroughly, using a large rubber spatula (mousse will begin to thicken while you're folding). Divide among 8 to 10 ramekins or wineglasses, each with a capacity of about 2/3 cup. Chill at least 3 hours, covering tightly when cold. Keep refrigerated until serving time for up to 4 days.

To serve, garnish each mousse with a spoonful (or small rosettes) of lightly sweetened whipped cream, then sprinkle some freshly-grated lime zest on top.

Variation: For a White Chocolate-Key Lime Mousse Pie, preheat oven to 350 degrees F. For the crust, combine in medium bowl 1 cup graham cracker crumbs and 1/3 cup whole unblanched (skin-on) almonds ground with 2 Tbsp. granulated sugar (in a food processor fitted with a steel blade). Mix well, then add 5 Tbsp. unsalted butter, melted. Combine thoroughly. Use about two-thirds of crust mixture for sides of crust in 9-inch heatproof glass pie plate, forming a high standing rim slightly above edge of pie plate. Firmly compact remaining crust mixture on bottom of pie plate. Bake in preheated oven for 7 to 8 minutes. Cool completely. Proceed with recipe as above. When whipped white chocolate mixture has been folded into lime curd, turn mousse into cooled crust. Chill at least 3 hours, covering tightly after 2 hours. Serve garnished with lightly sweetened whipped cream and sprinkled with lime zest. Serve within a day or two (the crust diminishes in quality after that time). 8 to 10 servings.

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