1. Heat oven to 350 degrees F. Line depressions of 2 jumbo muffin pans (12 total) with paper or foil liners.
2. Into small bowl, sift flour, cocoa and baking powder. In large bowl, beat butter until smooth. Beat in sugar until fluffy, 3 minutes. Beat in eggs, one at a time.
3. In small bowl, stir together milk, liqueur and vanilla.
4. On low speed, alternately beat flour mixture and milk mixture into butter mixture, beginning and ending with flour. Divide batter among prepared cups, about 1/2 cup each. Unwrap truffles; press one down to bottom of each cupcake and spread batter over top of truffle to cover.
5. Bake in 350 degree F oven until tops spring back when lightly pressed, 25 minutes. Let cupcakes cool in pan on wire rack 5 minutes. Remove cupcakes to rack; let cool.
6. Frost each with 1 rounded tablespoon hazelnut spread. Garnish with nuts. Store in airtight container for 1 week. Makes 12 cupcakes.