Mix the brown sugar, cinnamon, and salt together in a large bowl. Stir in the melted butter, then gently mix in the flour, being careful not to overmix (you just want to moisten the flour and mix until there is no visible dryness).

Squeeze a handful of the topping into your hand. If it doesn’t clump together, add a little more melted butter until it does.

Place in the refrigerator while making the cake

In a large bowl, beat the softened butter until smooth and fluffy (about 2 minutes).

Gradually add the powdered sugar, beating on low at first, then increasing speed to medium until well combined.

Add heavy cream (or milk) 1 tablespoon, beating until the buttercream is smooth and fluffy.

Preheat your oven to 350°F. Grease two 9-inch cake pans with cooking spray and line the bottoms with parchment paper.

In a medium bowl, whisk flour, cornstarch, baking powder, baking soda, nutmeg, and salt

In the stand mixer bowl, cream the softened butter and brown sugar until light and fluffy (about 2–3 minutes).

Beat in the eggs, one at a time, mixing until fully incorporated.

Alternately, add the flour mixture and the sour milk to the butter mixture, starting and ending with the dry ingredients. Mix just until combined—do not overmix. The batter should be smooth but thick.

Divide the batter evenly between the two prepared cake pans. Use a spatula to spread it evenly across the pans.

Sprinkle crumb topping evenly across the top of one of the cake layers. Make sure the topping is spread out to the edges of the pan. If it is all together, it will cause the cake to sink in the middle.

Bake for 25 minutes or until a toothpick inserted into the center of the cake comes out clean and the top is golden brown. The layer with crumble make take an extra 5-10 minutes

Let the cakes cool in the pans for 30 minutes, then transfer them to a wire rack to cool completely

Once cakes are completely cooled, spread the strawberry cream across the layer of cake without the crumbs. Gently place the crumb cake layer on top.