Cream the butter and sugar in a large bowl until light. Beat in eggs and vanilla; set aside.
Sift the cocoa, flour, salt, baking powder, and baking soda together. Stir the dry ingredients thoroughly into the butter mixture.
Cover the bowl with plastic wrap and refrigerate for 2 or 3 hours.
Preheat oven to 375F and butter 2 cookie sheets.
Using a teaspoon measure, roll level teaspoons of the dough into balls and place them 2 inches apart on the cookie sheets.
Bake for 10 to 15 minutes or until cookies are puffed and surfaces slightly dry and cracked.
Cool on racks.
To make the filling, cream the butter until light. Beat in the vanilla and powdered sugar, adding whipping cream and continuing to beat until the consistency of creamy frosting.
When the cookies are cooled completely, spread about 1/2 tablespoon of filling on the bottom of one cookie, then top with the bottom side of another cookie.
Makes about 3 dozen cookie sandwiches.
Not a NESTLÉ®-tested recipe.