6tablespoons(85 g) cold unsalted butter, cut into cubes
¾cup(94 g) all-purpose flour
¼cup(20 g) old fashioned rolled oats
½cup(100 g) granulated sugar
Pinchof salt
Apple Cake
1 ¼cups(156 g) all-purpose flour
1teaspoonbaking powder
1teaspoonground cinnamon
¼teaspoonsalt
½cup(113 g or 1 stick) unsalted butter, room temperature
½cup(100 g) granulated sugar
2large eggs, room temperature
1Tablespoonpure vanilla extract
3Tablespoonsmilk, room temperature
3Granny Smith apples, peeled and thinly sliced
Custard Sauce
6large egg yolks, room temperature
6Tablespoons(75 g) granulated sugar
1 ½cups(360 ml) whole milk
1 ½teaspoonspure vanilla extract
Instructions
Preheat oven to 350° F. Line a 9-inch springform pan with parchment paper round and grease with nonstick spray. Set aside.
Crumble Topping
Whisk together the flour, oats, sugar and salt. Add butter and use a pastry cutter (or two forks) to cut it into the dry ingredients until a sand-like mixture forms. Keep streusel in the refrigerator while preparing the cake batter.
Apple Cake
In a large bowl, whisk together flour, baking powder, cinnamon and salt. Set aside.
In a separate large bowl, beat butter and sugar until creamy, about 1 minute. Beat in eggs one at a time, then mix in vanilla and milk. Scrape down the sides and bottom of the bowl as necessary. Add flour mixture and mix just until combined. The batter will be thick.
Transfer batter to prepared pan. Arrange apple slices on top in one layer. Sprinkle streusel on top.
Bake at 350° F for 55 to 60 minutes. Let the cake cool in the pan for about 15 minutes before running a knife along the edge and removing the sides of the springform pan. Cool completely.
Custard Sauce
In a medium bowl, whisk together egg yolks, sugar and vanilla until pale, about 2 minutes. Set aside.
In a medium saucepan, heat milk until scalding hot (the edges of the pan will just start to simmer).
Temper the egg yolks. Slowly pour about ½ cup of the hot milk into the bowl of the egg mixture, whisking constantly. Pour egg mixture back into the saucepan, again whisking constantly.
Continue cooking the custard over medium heat until the custard thickens, about 4 minutes. Remember to stir constantly so the mixture doesn’t burn. Custard is done when it coats the back of a spoon. Transfer to a sauce boat or serving bowl.
Slice the cake and serve with a drizzle of custard sauce.
Notes
Streusel: Make sure the butter is cold. If it is warm then it will quickly melt into the cake and won't stay crisp on top.Apples: Granny Smith are best for baking. They keep their crisp texture and flavor under the high heat of the oven. Other good options are Braeburn and Honeycrisp.Store covered at room temperature for up to 2 days or in the refrigerator for 5 days.Freeze after the cake has cooled completely. Wrap in plastic wrap and place in an airtight container or bag. Freeze for up to 2 months. Defrost in the refrigerator before bringing to room temperature and serving.