Preheat oven to 175°C (350°F). Grease a cake pan. Line bottom of a pan with parchment paper.

Melt 1/2 cup butter, mix with 1/2 cup brown sugar and 2 tbsp cinnamon.

Spread mixture in pan. Arrange nectarine slices in a circular pattern on top.

Sprinkle 2 tbsp cornstarch over nectarines.

For cake: Cream brown butter, oil, white sugar, and 3/4 cup brown sugar.

Beat in eggs, yolk, and vanilla until smooth.

Sift together AP flour, cake flour, salt, baking powder, and baking soda.

Add dry ingredients to wet, alternating with milk and sour cream.

Pour batter over nectarines. Smooth the top.

Bake for about 45 minutes, or until a toothpick comes out clean.

Cool slightly, then invert onto a plate to serve.