Preheat the oven to 350° Fahrenheit. Spray three 8-inch round cake pans with cooking spray. Add round parchment paper to the bottom of the pans.
Sift the flour, cornstarch, baking powder, and salt into a medium bowl. Whisk it to make sure it is evenly mixed and set it aside.
Add the apple cider vinegar and milk to so a cup or small bowl and mix it together. Set it aside.
Using a the paddle attachment on a stand mixer, beat the butter and sugar for 3 minutes (make sure to stop the mixer and scrap the sides a few times). It should be light and fluffy.
Start the mixer on medium speed and add the 2 whole eggs. Once that is incorporated, gradually add the remaining 4 egg whites. Scrape down the sides of the bowl between each addition. Continue to beat on medium-high speed for 3 minutes.
Next, add the sour cream and vanilla. Mix on medium-high speed for another 2 minutes.
On low speed add approximately ⅓ of the flour mixture and ½ of the milk/apple cider vinegar mixture. Repeat until all the flour and milk have been combined (ending with the flour: ⅓ flour ½ milk ⅓ flour ½ milk ⅓ flour).
Scrape down the sides and mix for another 15 seconds.
Divide the batter evenly between the three 8-inch circle cake pans. Bake for 20-24 minutes. If you insert a toothpick in the center it should have crumbs attached and not any wet batter.
Let the cake cool in the pan for 10 minutes. Then allow them to finish cooling on a wire cooling rack.
For the Frosting
Using the whisk attachment on your mixer, beat the butter on medium speed for about 30 seconds, scrape the sides and beat for another 30 seconds.
Add the powdered sugar 1 tablespoon at a time on medium speed until it has all be added (scrap the sides as necessary)
Add the vanilla and strawberry jam and mix until it is incorporated. Scrape down the sides. If the consistency of the frosting is soft you don't need to add the optional milk. Whip for another 3 minutes until it is light and fluffy.
For the Crunch Topping
Add the freeze fried strawberries and Golden Oreos to a food processor. Use the pulse setting until they are broken into large crumbs.
Add the melted butter and pulse a few more times until it is all combined.
Assembling the Strawberry Shortcake Crumb Cake
Place the first 8-inch round cake on a cake plate. Pipe a thin rim of strawberry frosting around the edges and fill in the middle. Add the thinly sliced fresh strawberries to the layer.
Top with the next cake layer and repeat the previous step.
Place the third cake layer on top. Apply a thin layer of frosting around the entire cake to lock in the crumbs. Freeze the cake for about 10-15 minutes to set the crumb coat.
Continue frosting your cake, adding buttercream to the sides. Use a cake scraper to make the sides even. Next, add the buttercream to the top and use an offset icing spatula to make that even.
Add the strawberry shortcake crunch topping to the sides. Slice some fresh strawberries for the top of the cake.
Notes
Tips:
Make sure the eggs, milk, and sour cream are at room temperature. It helps it to mix evenly into the batter and rise more easily.
Gently wrap your cake layers in plastic wrap and freeze them before frosting. This makes the cake stiffer and produces fewer crumbs.
Storage: Store leftover cake in an airtight container. Remove the fresh strawberries from the top for storage. It will last at room temperature for 3 days and in the refrigerator for up to 5 days.
Freezing: You can freeze the whole cake or individual slices for up to 3 months. To freeze cake, wrap it in plastic wrap followed by aluminum foil. Then put it into an airtight container or freezer bag.
Thawing: Allow the cake to thaw in the refrigerator for 8 hours before consuming.