Preheat the oven to 350°F (175°C). Grease a 9-inch round cake pan (or 9x9 square) and line the bottom with parchment paper. Lightly butter the parchment.

Dry ingredients

In a medium bowl, whisk together 2 cups all-purpose flour, 1 cup granulated sugar, 2 teaspoons baking powder, 2 teaspoons ground cinnamon, and 1 teaspoon fine salt until evenly combined.

Wet ingredients

In a large bowl, whisk the 2 large eggs until lightly frothy. Add 3 tablespoons whole milk, 1 teaspoon vanilla extract, and 1 cup melted unsalted butter (slightly cooled). Whisk until smooth and combined.

Combine batter

Add the dry ingredients to the wet ingredients in two additions, folding with a rubber spatula until just combined. Do not overmix; a few small streaks are okay. The batter will be fairly thick.

Apples & Topping

Prepare apples

Peel, core, and thinly slice 3 apples. Toss the slices in a bowl with 1 tablespoon lemon juice, 2 teaspoons granulated sugar, and 1 teaspoon ground cinnamon to prevent browning and add flavor.

Assemble cake with apples

Pour the batter into the prepared pan and smooth the top. Arrange the apple slices over the batter in a single overlapping layer, covering as much of the surface as possible. Sprinkle the apples with 2 tablespoons light brown sugar and dot with 1 tablespoon butter pieces.

Bake

Bake in the preheated 350°F (175°C) oven for 40–50 minutes, or until a toothpick inserted into the center (between apples) comes out with a few moist crumbs but not wet batter. If the apple tops brown too quickly, tent loosely with aluminum foil for the last 10–15 minutes.

Cool

Remove from oven and let the cake cool in the pan on a wire rack for 15 minutes. Run a thin knife around the edge, then invert onto the rack (peel off the parchment) and flip right-side up. Cool another 20–30 minutes before drizzling with caramel (cake should be warm but not hot).

Caramel Drizzle

Make caramel sauce

Place 1 cup granulated sugar and 2 tablespoons water in a medium heavy-bottomed saucepan over medium heat. Swirl the pan gently (don’t stir) until the sugar dissolves and begins to caramelize to a deep amber color, about 6–9 minutes. Watch closely to avoid burning.

Finish caramel

When sugar reaches deep amber, remove from heat and carefully add 4 tablespoons unsalted butter, whisking until melted. Slowly pour in 6 tablespoons warmed heavy cream while whisking (mixture will bubble vigorously). If desired, stir in 1 teaspoon fine sea salt. Return briefly to very low heat to smooth the sauce if needed, then let cool 5–10 minutes until slightly thickened but still pourable.

Drizzle and serve

Place the cooled cake on a serving plate. Using a spoon or a small pitcher, drizzle the warm caramel evenly over the apple-topped cake. Slice and serve. Leftover caramel can be refrigerated in a jar for up to 2 weeks; gently warm before using.