Step 1: Make the Cupcake Batter

1. Preheat the Oven: Set your oven to 350°F (175°C) and line a muffin tin with cupcake liners.
2. Mix Dry Ingredients: In a bowl, whisk together flour, baking powder, and salt.
3. Cream Butter & Sugar: In a separate bowl, beat butter and sugar until light and fluffy.
4. Add Eggs & Vanilla: Mix in eggs one at a time, beating well after each addition. Stir in vanilla extract.
5. Combine Wet & Dry Ingredients: Gradually add the dry ingredients to the butter mixture, alternating with milk, until just combined.

Step 2: Bake the Cupcakes

1. Fill the Liners: Spoon the batter into cupcake liners, filling each about ⅔ full.
2. Bake: Place in the oven and bake for 18-20 minutes, or until a toothpick inserted in the center comes out clean.
3. Cool Completely: Remove from the oven and transfer the cupcakes to a wire rack to cool.

Step 3: Prepare the Custard Filling

1. Heat the Milk: In a small saucepan, whisk together milk, sugar, and cornstarch over medium heat.
2. Thicken the Custard: Continue whisking until the mixture begins to thicken.
3. Add Egg Yolk & Vanilla: Remove from heat and quickly whisk in egg yolk and vanilla extract until smooth.
4. Cool Completely: Transfer the custard to a bowl and refrigerate until completely cool.

Step 4: Fill the Cupcakes

1. Core the Cupcakes: Use a knife or cupcake corer to cut out a small hole in the center of each cupcake.
2. Fill with Custard: Spoon the cooled custard into each hole until filled.

Step 5: Make the Chocolate Glaze

1. Heat the Cream: In a small saucepan, heat heavy cream over medium heat until just simmering.
2. Melt the Chocolate: Remove from heat, add chocolate chips, and stir until smooth and glossy.

Step 6: Glaze the Cupcakes

1. Dip the Tops: Carefully dip the top of each cupcake into the warm chocolate glaze, letting the excess drip off.
2. Let the Glaze Set: Allow the cupcakes to sit for a few minutes until the glaze is firm and glossy.