3Granny Smith apples, peeled, cored, and diced (about 3 cups)
Streusel Topping
3/4cupall-purpose flour
1/2cupgranulated sugar
1/4cuprolled oats
6tablespoonsunsalted butter, cold and cubed
Custard Sauce
1 1/2cupswhole milk
5large egg yolks
1/3cupgranulated sugar
1tablespooncornstarch
2teaspoonspure vanilla extract
1/2cup whole milk
Instructions
PREPARE OVEN: Preheat the oven to 375°F. Spray an 8-inch round cake pan with nonstick spray.
MIX DRY INGREDIENTS: In a medium bowl, whisk together 1 1/4 cups all-purpose flour, 1 teaspoon baking powder, 1 teaspoon ground cinnamon, and 1/4 teaspoon kosher salt. Set aside.
CREAM BUTTER: In a large mixing bowl, beat 1/2 cup unsalted butter, room temperature and 1/2 cup granulated sugar on medium-high speed until light and fluffy.
ADD WET INGREDIENTS: Add 2 teaspoons pure vanilla extract, then beat in 2 large eggs, room temperature one at a time. Mix in 1/4 cup whole milk until combined.
FINISH BATTER: Reduce mixer speed to low and mix in the flour mixture just until combined. Fold in 3 Granny Smith apples, peeled, cored, and diced.
TRANSFER BATTER: Pour the batter into the prepared pan and spread evenly.
MAKE STREUSEL: In a medium bowl, whisk together 3/4 cup all-purpose flour, 1/2 cup granulated sugar, and 1/4 cup rolled oats. Cut in 6 tablespoons unsalted butter, cold and cubed until pea-sized crumbs form.
TOP AND BAKE: Sprinkle the streusel evenly over the batter. Bake for 50 to 55 minutes, until golden brown and a toothpick inserted in the center comes out clean.
COOL CAKE: Remove from the oven and cool completely in the pan.
HEAT MILK: For the custard sauce, add 1 1/2 cups whole milk to a large saucepan. Heat over medium-high until just simmering, then remove from heat.
WHISK EGGS: In a mixing bowl, whisk together 5 large egg yolks and 1/3 cup granulated sugar until pale.
TEMPER: Slowly whisk the hot milk into the egg mixture. Return everything to the saucepan.
THICKEN: In a small bowl, whisk 1/2 cup whole milk with 1 tablespoon cornstarch. Stir into the saucepan. Cook over medium-low heat, stirring constantly, until thickened enough to coat the back of a spoon.
FINISH SAUCE: Remove from heat, whisk in 2 teaspoons pure vanilla extract, then strain to remove any lumps.
SERVE: Slice the cake and serve warm or at room temperature with custard sauce.
Notes
Make-Ahead: The cake can be made up to 4 days ahead and stored at room temperature in an airtight container.Storage: Store custard sauce separately in the refrigerator for up to 3 days.Reheating: Warm custard gently in the microwave in short intervals, stirring between each.Apple Tip: This cake is meant to be apple-heavy. The apples soften during baking and give the cake its signature texture and flavor.No Sauce Option: Skip the custard and dust the cake with powdered sugar for a lighter breakfast-style treat.