Place a medium mixing bowl and the beaters of your electric mixer in the refrigerator to chill for at least 30 minutes.
MAKE THE MOUSSE: Combine the rhubarb and sugar in a medium saucepan. Cover and bring to a simmer over low heat. Cook for 8 to 10 minutes, or until the rhubarb is very soft. Transfer to the bowl of a food processor and puree. Transfer the puree to a medium nonreactive mixing bowl and set aside.
Put 2 tablespoons cold water in a small saucepan and sprinkle the gelatin over. Set aside and let soften for 5 minutes. Heat the mixture over low heat, swirling until the gelatin is completely dissolved and no grains remain. Stir the gelatin into the pureed rhubarb and allow to cool. Then fold the sour cream and berries into the puree.
In the chilled bowl, whip the cream with an electric mixer at high speed until it holds soft peaks. Do not overbeat. Gently fold the whipped cream into the fruit mixture with a rubber spatula. Cover the mousse and refrigerate until it sets, about 4 hours, or overnight.
MAKE THE SAUCE: Combine the raspberries and confectioner's sugar in a small saucepan. Cook over low heat until the berries are soft, about 3 to 4 minutes. Transfer to a food processoror blender and puree. Strain through a fine-mesh strainer into a small bowl and discard the seeds. Stir 2 tablespoons of cold water into the suace to thin. Transfer to a jar and refrigerate.
PREPARE THE MOLDING CHOCOLATE: Put both chocolates in the top of a small double boiler over simmering water. Melt over low heat, stirring constantly with a spatula or wooden spoon until the chocolate is very smooth and shiny. Remove from the heat and add the corn syrup and liquor. Using a wooden spoon, mix the chocolate vigorously (the chocolate will start to "seize"; don't worry, be happy, you're doing just fine) until the chocolate gradually thickens and leaves the sides of the bowl to form a loose, soft mass. The stirring should take no longer than a minute; do not overwork the chocolate or its oils may separate.
Divide the chocolate into 2 equal portions. Place one portion in the center of an 11 by 16 inch long sheet of plastic wrap on a cool flat surface. Level the chocolate with a spatula. Cover the chocolate with a second sheet of plastic wrap the same size as the first sheet. Using a rolling pin, gently roll the chocolate into a rectangle about 10 by 15 inches and 1/16 inch thick. Leaving the chocolate still covered, set aside at room temperature away from any heat source for 30 to 45 minutes to prtially set. Repeat with remaining chocolate. When the chocolate is partially set, it should be no longer wet by still very pliable. If at first it's still too wet to handle, let it sit for about 5 minutes more but do not allow it to harden or it will become difficult to knead.
Remove the plastic wrap from one sheet of chocolate. Generously dust a work surface with confectioner's sugar. Gather the chocolate into a ball. If the chocolate has dried out and cracks or crumbles a little, don't be concerned, the chocolate will soften and come togther again after kneading. Knead it briefly, pressing it into the confectioner's sugar as you knead, until soft and no longer sticky. If it feels sticky, knead in a little more confectioner's sugar. The molding chocolate should feel very soft and smooth.
Divide the chocolate in half and shape each half into a ball. Cover the balls with plastic wrap and set aside. Knead and shape the remaining sheet of chocolate in the same manner, for a total of 4 chocolate balls.
ASSEMBLE THE PURSES: Brush off any chocolate crumbs left on the work surface; the surface should be dry, or the chocolate will stick. Lightly dust the work surface and a rolling pin with confectioner's sugar. Slightly flatten one chocolate ball and gently roll it out into a circle about 9 inches in diameter. As you roll the chocolate, be sure to lift it from time to time and dust the surface underneath with a little more confectiner's sugar to prevent the chocolate from sticking.
Place one quarter (about 1/3 cup) of the mousse in the center of the chocolate circle. Gather the sides up to enclose the filling. Pinch the purse at the neck to seal in the mousse, allowing the top edges of the purse to fan out. Transfer the purse to a large platter, loosely cover with plastic wrap, and refrigerate.
Repeat rolling and filling the remaining balls of chocolate to make 3 more purses. Cover and refrigerate until ready to serve.
TO SERVE: Place a chocolate purse on each chilled dessert plate and spoon some raspberry sauce around it.