Pre-heat the oven to 375. Take an 8 x 8 baking dish and spray it liberally with cooking spray. Then prepare the crumb topping first. Combine all of the ingredients in a mixing bowl, with the butter going in last. Stir it all together thoroughly until it is a uniform mixture. Set it aside.

In a large mixing bowl whisk the flour, sugar, baking powder, cinnamon, nutmeg and salt together to aerate them. In another bowl whisk the melted butter, milk, mascarpone, eggs and vanilla together until smooth. Pour the wet ingredients into the bowl of dry ingredients and whisk together just until a smooth batter forms. Switch to a spatula and gently fold in the blueberries.

Pour the batter into the prepared baking dish and even it out with the spatula. Distribute the crumb topping in an even layer on top of the batter, letting it slightly sink in. Get the baking dish into the oven for the cake to bake for around 50-55 minutes. A toothpick inserted in the center should come out clean.

Let it cool for a few minutes, then just cut into slices and serve! It's so amazing for brunch with a great cup of coffee or tea.