With the melted butter, brush 6 (3/4-cup) dariole * cups. Line the bottom of each cup with a circle cut from waxed paper and butter the circles. Arrange the cups on a flat baking tray and set aside.

In the large bowl of an electric mixer, using the whisk, whisk together the egg yolks and sugar on high speed until the mixture is pale yellow, almost white, and very thick.

Meanwhile, in a saucepan, bring 1 1/2 cups of the cream to a boil. With the mixer on low speed, slowly pour the cream into the egg yolk mixture and continue to whisk until completely incorporated. Divide into 2 equal portions, and refrigerate, covered, until needed.

In a clean bowl, with a clean whisk, whip the remaining 1/2 cup cream to soft peaks. Refrigerate, covered, until needed. When ready to use, whisk slightly to return to the soft peak stage.

Melt the white chocolate in the top of a double boiler or small heat-proof bowl placed over very lightly simmering water. Turn off the heat when the chocolate is almost melted and let the bowl sit over the water to finish melting. Stir occasionally. In a small saucepan, bring 1 of the egg yolk mixtures just to a boil, stirring all the while. Strain into a clean bowl of the mixer. With a rubber spatula, scrape in the melted white chocolate, add the instant coffee, and with the whisk, whisk until the bottom of the bowl feels cool to the touch. Alternately, you can place the mixture in a bowl over ice water and whisk until cooled to cool the mixture faster. Refrigerate, covered, for about 30 minutes. Remove from the refrigerator and fold in about 1/2 of the softly whipped cream. For easier pouring, transfer to a pitcher and divide among the prepared cups. Place in the freezer for at least 1 hour.

Melt the milk chocolate in the top of a double boiler or small heat-proof bowl placed over very lightly simmering water. Turn off the heat when the chocolate is almost melted and let the bowl sit over the water to finish melting. Stir occasionally. In a small saucepan, bring 1 of the egg yolk mixtures just to a boil, stirring all the while. Strain into a clean bowl of the mixer. With a rubber spatula, scrape in the melted white chocolate, add the instant coffee, and with the whisk, whisk until the bottom of the bowl feels cool to the touch. Alternately, you can place the mixture in a bowl over ice water and whisk until cooled to cool the mixture faster. Refrigerate, covered, for about 30 minutes. Remove from the refrigerator and fold in about 1/2 of the softly whipped cream. For easier pouring, transfer to a pitcher and divide among the prepared cups. Remove the frozen white chocolate mousse from the freezer. Top with some of the chopped cookies. Top with the milk chocolate mixture. Return to the freezer and freeze for at least 3 more hours. This can be made several days in advance.

When ready to serve, remove the tray from the freezer and run a sharp knife around the mousse, as close to the sides of the cup as possible. Turn the cups upside down onto a flat surface, tap the tops a few times, and unmold. Remove the waxed paper circles.

*Dariole cups can usually be purchased in shops that carry gourmet kitchen equipment. However, if not available, you can use large demitasse cups, coffee cups, or water glasses.