Preheat your oven to 180°C / 350°F and line a 10×6.5-inch or 8×8-inch baking pan with parchment paper for easy removal after baking.

Chop the apples into roughly ½ inch (1.25 cm) pieces.

In a small bowl, combine the sugar, cinnamon, and melted brown butter for the topping, then set it aside.

In a large mixing bowl, whisk together the eggs, oil, sour cream (or Greek yogurt), milk, both sugars, vanilla, and salt until the mixture is smooth and well blended.

Sift the cake flour, baking powder, and baking soda directly into the bowl with the wet ingredients.

Switch to a spatula and gently fold the dry ingredients into the wet mixture, using light motions to avoid overmixing.

When most of the flour is incorporated (a few streaks are fine), fold in the chopped apples until they are evenly distributed.

Once the apples are mixed in, the batter should be fully combined and smooth.

Pour the batter into the prepared baking pan and smooth the top with the back of your spatula for even baking.

Sprinkle the prepared cinnamon sugar evenly over the top of the batter.

Bake the cake for 35–40 minutes, or until the top is golden and crisp, springs back when gently pressed, and a toothpick inserted into the center comes out clean or with a few cooked crumbs.

Remove the cake from the oven and let it cool in the pan for about 10 minutes before slicing.

Serve warm, or allow it to cool completely and top with the optional whipped brown butter mascarpone cream.

To make the whipped cream, cream the solid brown butter in a stand mixer or with a hand mixer until smooth.

Add the mascarpone, cream cheese, vanilla, and salt, then beat on medium-low until well combined, scraping down the sides as needed.

Incorporate the honey and beat until evenly mixed.

If you prefer a lighter cream, add a few tablespoons of heavy cream and beat on medium until it reaches your desired whipped texture.