1/2 cup (1 stick) unsalted butter, plus more for pan
1 and 1/2 cups all purpose flour, plus more for pan
1 and 1/2 teaspoons baking powder
1/2 teaspoon salt
3 large eggs, room temperature
1 cup sugar
1/2 cup whole milk
1 teaspoon pure vanilla extract
1 and 1/2 cups thick fruit jam (raspberry, or strawberry, etc.)
6 ounces semi-sweet chocolate, finely chopped
1 tablespoon light corn syrup
2/3 cup heavy cream
Make cake: Preheat oven to 350 degrees. Butter and flour a 9-inch round cake pan (2 inches deep). In a medium bowl, whisk together flour, baking powder, and salt. In a large bowl, using an electric mixer, beat eggs and sugar on high until pale and fluffy, 5 minutes. In a small saucepan, bring milk and butter to a simmer over medium. With mixer on medium, gradually add flour mixture to egg mixture and beat just until combined. With mixer on low, add milk mixture in a steady stream and beat until combined. Fold in vanilla.
Pour batter into pan. Bake until top is light golden and toothpick inserted in center of cake comes out clean, 35 to 40 minutes.
Let cool in pan on a wire rack, 10 minutes. Run a knife around edge of pan; turn cake out onto rack to cool completely (top side up), 30 minutes.
With a serrated knife, trim top of cake to make it level, then split cake in half horizontally. Place bottom layer on a cake plate or serving platter and spread jam evenly on top with an offset spatula. Top with second layer.
Make glaze: Place chocolate and corn syrup in a heatproof medium bowl. In a small saucepan, bring cream to a boil. Immediately pour over chocolate and let sit 2 minutes. Stir until mixture is smooth.
Pour glaze on cake and spread with an offset spatula so it drips down sides. Refrigerate until glaze is set, 45 minutes (or up to 2 hours).