To prepare the fruit: Combine the blueberries, 2 tablespoons sugar, lemon juice, cornstarch, and salt in a non-aluminum saucepan. (Aluminum reacts with the acid in the fruit and creates a peculiar taste.).
Bring to a boil and reduce the heat, simmering until the mixture thickens and a sauce forms, about 10 minutes. Stir occasionally to prevent sticking. Add the peaches and cook for 1 minute, then remove from heat, and gently fold in the raspberries and eau-de-vie. Set aside.
To prepare the biscuits: Preheat oven to 375 degrees F. In a food processor, place the flour, 2 tablespoons sugar, baking powder, and salt. Blend briefly. Add the butter and pulse until the butter is the size of peas.
Pour mixture into a bowl, add 1 cup of the cream, and combine with a fork until moistened. Immediately turn out onto a lightly floured board and knead about 10 times. Small lumps of butter should be visible.
Roll out to a 3/4-inch thickness. Keep dough in a square shape. Cut into 6 pieces and place on an ungreased cookie sheet. (You can do this either with a knife, for square biscuits, or with biscuit cutters for round ones. If you don’t have biscuit butters, you can also use one end of a clean 8-oz tomato sauce can.).
Mix the egg yolk with 2 tablespoons of cream and 1/2 teaspoon vanilla, and brush on the tops of the biscuits. Sprinkle with 2 tablespoons sugar. Bake 15 to 20 minutes or until golden brown.
To make the whipped cream: Add the remaining 2 tablespoons of sugar to the remaining 1 cup of whipping cream, along with 1/2 teaspoon vanilla extract. Beat until soft peaks form. Refrigerate. (It is helpful if, before adding the cream, sugar and vanilla to the bowl you have first chilled the bowl in the freezer for about 10 minutes.).
To assemble: When cool, split the biscuits and place the bottom half of each onto a plate or in a bowl. Add one-sixth of the berry mixture, and garnish with a dollop of whipped cream. Place the tops on, slightly off-center, and serve immediately.