In a medium heatproof bowl, whisk together the granulated sugar, salt, and cornstarch. Add the egg yolks and ¼ cup of the milk, whisking until the mixture is smooth and well combined. Set aside.

In a medium saucepan, heat the remaining 1 ¾ cups of milk over medium heat until it just begins to simmer. Do not allow the milk to boil. Remove from heat.

Gradually temper the egg mixture by slowly pouring approximately ½ cup of the hot milk into the yolk mixture while whisking continuously. Once tempered, return the egg mixture to the saucepan with the remaining milk, whisking constantly.

Return the saucepan to medium heat and cook, stirring continuously with a wooden spoon, until the mixture thickens and begins to bubble, about 5 minutes. Remove from heat and stir in the butter and vanilla extract until fully incorporated.

For a smooth texture, strain the pastry cream through a fine-mesh sieve into a clean bowl. Cover with plastic wrap pressed directly onto the surface and refrigerate for at least 2 hours or up to 24 hours.

Preheat the oven to 325°F (165°C). Grease two 9-inch round cake pans, line the bottoms with parchment paper, and grease again. Set aside.

In a small bowl, whisk together the flour, baking powder, and salt.

In a large mixing bowl or stand mixer fitted with the whisk attachment, beat the eggs and granulated sugar on medium-high speed for approximately 4 minutes, until the mixture becomes pale and thick and falls from the whisk in ribbons. Mix in the vanilla extract.

Gradually add the dry ingredients on low speed, mixing just until combined.

In a microwave-safe measuring cup, heat the milk and butter together until the butter is melted and the milk is hot and lightly steaming. Slowly add the hot milk mixture to the batter while mixing on low speed, just until incorporated. The batter will be thin.

Divide the batter evenly between the prepared pans. Bake for 28–33 minutes, or until a toothpick inserted into the center comes out clean.

Allow the cakes to cool in the pans for 20 minutes, then turn out onto a wire rack to cool completely.

Remove the pastry cream from the refrigerator approximately 20 minutes before assembly to soften slightly.

Place one cake layer onto a serving plate. Spread the pastry cream evenly over the surface, leaving a ½-inch border around the edge.

Place the second cake layer on top, bottom side up, and gently press down. Refrigerate the assembled cake while preparing the chocolate glaze.

In a microwave-safe bowl, heat the heavy cream and corn syrup until steaming, stirring every 20 seconds. Add the chopped chocolate and allow it to sit undisturbed for 5 minutes.

Stir until smooth and fully melted. Pour the glaze over the center of the cake and spread evenly with an offset spatula, allowing some glaze to drip down the sides if desired.

Refrigerate the cake for at least 2 hours to set. Before serving, allow the cake to sit at room temperature for approximately 30 minutes. Slice using a warm knife for clean cuts.