Preheat the oven to 375 F. Spray non-stick cooking spray in an 8×8 glass pan. Set aside.
In a medium-sized bowl, whisk together the flour, sugar, baking powder, and salt. Set aside.
1 cup flour, 1/2 cup sugar or monk fruit sweetener, 2 teaspoons baking powder, 1/2 teaspoon salt
In a small mixing bowl, whisk together the milk, melted butter, and eggs. Pour the wet ingredients into the dry ingredients and mix until combined.
2 eggs, 1/2 cup milk, 2 Tablespoons oil or melted butter
Pour the cake batter into the greased pan. Top with the raspberries. Set aside.
2 cups raspberries
In another small bowl, add all the topping ingredients: flour, sugar, oatmeal and cold butter. Using a pastry cutter, fork, or your hands "cut" the butter into the dry mixture until a crumbly texture forms. Pour the crumb topping over the blueberries and smooth until level.
1/2 cup flour, 1/2 cup oatmeal, 1/2 cup white sugar or monk fruit (See notes as to why we prefer regular sugar in the topping), 1/4 cup cold butter, cut into large chunks
Bake for 45 to 50 minutes, uncovered, or until the cake is fluffy and a toothpick inserted in the middle of the cake comes out clean.
Allow the cake to cool for 30 minutes before slicing. Store leftovers in an airtight container at room temp for up to 3 days.