Above was adjusted for a bit more sugar and 1/2 butter, 1/2 oil

Make Struesel Topping and Custard Sauce first or ahead of time.

CAKE: Preheat oven to 375 F. Butter a 9 spring form pan and fit bottom with a round of parchment paper. Butter the parchment paper and sides.

In a large bowl whisk flour, baking soda, baking powder, salt, cinnamon, and nutmeg.

Peel, core and chop apples into chunky bite-size pieces. Add ONE-HALF to the flour mixture and stir to combine. Set aside.

Separate eggs so you have 2 egg yolks in one bowl and 4 egg whites in a separate bowl. Save other 2 yolks for custard.

In another bowl, beat the butter, oil, and sugar on medium-high for 1 minute. Add yolks, buttermilk, and vanilla and beat for 1 minute longer. Scrape batter into the flour mixture and stir just until all the ingredients are combined and all the dry ingredients are moistened.

In a clean bowl with clean beaters, beat egg whites until foamy. Sprinkle 2 tablespoons sugar and continue beating until stiff peaks form. Using a rubber spatula gently fold the egg whites into the cake batter just until combined . Dont overmix. OK if streaks of egg white in batter. Scrape into prepared pan. Distribute remaining apples over top pressing lightly.

Bake on a sheet pan for 50-60 minutes or until toothpick comes out clean. Remove and let cool completely on a wire rack before removing the sides of the pan.

CUSTARD SAUCE: Pour milk into a heavy-bottomed medium-size saucepan and heat over medium until bubbles appear along the edges. Meanwhile, whisk sugar and yolks with an electric mixer until the mixture is thickened slightly and pale yellow, about 3 or 4 minutes. Beat in the cornstarch.

With the mixer running, gradually pour the heated milk into the egg yolks in a thin steady stream. Stop the mixer halfway through pouring in the milk to quickly scrape down the sides of the bowl. Resume beating at medium speed to slowly add the remaining milk.

Pour the mixture back into the saucepan and cook over medium heat, stirring constantly with a wooden spoon or spatula, until the sauce thickens enough to coat the spoon. Do not let the mixture come close to boiling . The max temp should be 170 F.

Strain into a bowl and stir in the vanilla. Cover and refrigerate. Custard sauce can be served either warm or cold over individual slices.

STREUSEL: In a medium-sized bowl, whisk flour, brown sugar, granulated sugar, and salt

Drizzle butter over the mixture and use a fork to toss the ingredients together until flour absorbed but still clumpy. Dont over-mix or it will become a paste. Refrigerate.

Scatter evenly over muffins, pie, or coffee cake before baking. Adding streusel might add a minute or so to baking time.