You can find the entire recipe here. I broke this recipe down into three separate parts: the pastry, the filling, and the frosting
Preheat oven to 375 degrees. You will also need a 24 cup mini-muffin pan.
Pastry: Start with the pastry to give it time to chill before baking. Combine the flour, sugar, cocoa powder (I used Hershey's Special Dark Dutch Process Cocoa Powder) and salt in a food processor. Add 1/2 cup cold butter cut into cubes and process until crumbly. Add one egg yolk mixed with two tablespoons cold water and pulse processor until a dough ball forms (you may need to add a bit more water). Cover and refrigerate dough until firm enough to make into balls. When dough is firm, divide into 24 equal sized balls. Press one ball into each cup of the mini-muffin pan. When finished, place pan in fridge to chill.
Filling: In a small saucepan melt together the butter and chocolate until smooth. Remove from heat and stir in egg, sugar, raspberry liqueur (or raspberry extract or raspberry syrup) and vanilla extract. Remove mini-muffin pan from fridge and fill each pastry cup with one tablespoon of the filling and bake for around 12 to 15 minutes. Let pan cool for 10 minutes then run a sharp knife around the edgies of each tassie to loosen from pan. Remove the tassies from the pan and let cool completely on a wire rack.