Adjust the oven rack to the middle position and heat the oven to 350 degrees F—Pour 4 tablespoons of melted butter into a 3.1-quart nonstick rectangle cake pan, tilting to coat the bottom and sides. Whisk ¾ cup light brown sugar, 1 teaspoon cornstarch, 1 teaspoon pure almond extract, and 1 teaspoon pure vanilla extract together in a small bowl, then sprinkle evenly over the melted butter. Arrange pitted cherry over the sugar mixture, nesting cherries snugly together.

Sift together the flour and baking powder in a large bowl; set aside. Place the ¼ cup avocado oil, 1 stick unsalted butter, ¼ teaspoon kosher salt, 1 cup granulated sugar, and ½ cup light brown sugar in the bowl of a stand mixer fitted with the paddle attachment and beat on medium speed for about 3 minutes. Beat in the vanilla and almond extracts.

Beat in the eggs and egg yolk one at a time, ensuring they emulsify completely with the butter mixture. Reduce the mixer speed to low, scrape bowl and beater and add ½ of the dry ingredients, and add half the buttermilk and beat until just combined.

Next, add the remaining flour mixture and the buttermilk, and beat on low speed until just combined. Do not overmix the batter! Using a rubber spatula, fold it all by hand to ensure no lumps at the bottom of the bowl. Pour batter over the cherries in the pan and smooth the top with a rubber spatula.

Bake the Cherry Upside-Down Cake until deeply golden brown and a toothpick inserted in the center comes out clean, 50 to 55 minutes. Let the cake cool in the pan on a wire rack for 5 minutes. Run a knife around the pan's edge to loosen the cake's sides, then invert the cake onto a serving platter. Discard parchment paper. Let the cake cool for a least 1 hour. Serve warm or cool—store covered in the refrigerator for up to 3 days.