1. Preheat oven to 350 F. and arrange rack in center. Line 1 (12-cup) muffin pan with baking cups; set aside. Whisk together flour, baking powder and salt in a bowl; set aside. Beat together butter and granulated sugar in a large bowl on high speed until light and fluffy, about 2 minutes. Add eggs and extract; beat until combined well, about 2 minutes. Alternately add flour mixture and coconut milk, beginning and ending with flour mixture, beating until just combined.
2. Divide batter among baking cups and bake until cupcakes spring back when lightly touched, 18 to 20 minutes. Cool 10 minutes, remove cupcakes from pan and cool completely on rack.
3. Holding a small knife at an angle, cut a 1-1/2-inch round in the top of each cupcake forming a shallow cone-shaped opening. Remove tops and fill each cupcake with 2 tablespoons custard; re-cover. (Can be made ahead. Store in an airtight container, chilled, up to 2 hours.) Dollop whipped cream on top of each cupcake and garnish with coconut, if desired.