Preheat the oven to 375 and prepare an 8x8-inch pan with grease and parchment. Set to the side.
Make the crumb topping. In a medium-sized bowl, combine the sugar, flour, cinnamon, brown sugar, and melted butter. Use a fork to combine the mixture until crumbs start to form. Set to the side.
In a small bowl, combine the flour, baking powder, and baking soda. Set to the side.
In a large bowl with a hand mixer or in the base of a stand mixer with a paddle attachment, cream the butter with the sugar, vanilla, and eggs. Add in the buttermilk, alternating with the flour mixture. Mix until combined.
With a rubber spatula, fold in the blueberries.
Pour the cake batter into the prepared pan and top the cake with the crumb topping, distributing evenly over the top.
Bake the cake for 44-55 minutes until a toothpick runs clean.
Let the cake fully cool on a cooling rack to come to room temperature.
