1. Prepare the Crust:

1. Preheat oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners.
2. In a bowl, whisk together flour, baking powder, and salt. Set aside.
3. In a large bowl, beat butter and sugar until light and fluffy. Add eggs one at a time, then vanilla. Gradually add flour mixture alternately with milk, beginning and ending with flour. Mix until just combined.
4. Divide batter evenly among muffin cups (about 2/3 full). Bake 18-20 minutes until a toothpick inserted comes clean. Cool completely in pan.
5. For custard: In a small bowl, whisk egg yolks, sugar, and cornstarch. In a saucepan, heat milk until simmering. Gradually whisk hot milk into egg mixture. Return to saucepan and cook over medium heat, whisking constantly until thickened. Remove from heat, stir in vanilla and butter. Press plastic wrap onto surface and chill until cold.
6. For ganache: Heat cream until just simmering. Pour over chopped chocolate in a bowl. Let sit 1 minute then stir until smooth. Cool slightly until thick but pourable.
7. Once cupcakes are cool, use a small knife to cut a cone from the top of each. Fill cavity with custard, replace top (trim if needed). Spoon ganache over each cupcake. Let set for 15 minutes before serving.