In a medium bowl, use your hands to toss together all of the dry ingredients. Stir in the melted butter until evenly moistened with a mix of large and small clumps. Place in the refrigerator while we make the batter.

Preheat the oven to 350F and grease and line the bottom of a 9″ springform pan.

In a large bowl using an electric mixer or by hand, mix together the butter and sugar until light and fluffy. Then mix in the egg and vanilla, followed by the sour cream. Once smooth, mix in the baking powder, salt, and baking soda until evenly distributed.

Now prep the blueberries – In a medium bowl, toss together the blueberries and zest, then toss with the cornstarch until evenly coated.

Back to the batter – Use a silicone spatula to fold in the flour and just before it’s combined, add in half of the blueberries and fold to bring the batter together. It should be pretty thick.

Spread the batter in the springform pan and top with a single layer of the remaining blueberries. Then remove the crumble from the refrigerator and use your hand to break it up into fine crumbs. Top with the chilled crumble and bake for 45 to 50 minutes, or until the top is golden brown and the center is evenly puffed. The middle also shouldn’t move when the pan is nudged.

Allow the cake to cool for about 20 minutes at room temperature then transfer to the refrigerator until cooled, about 1 hour.

For the icing, whisk together all of the ingredients and drizzle over the cooled cake. Now slice and enjoy!

NOTE: Mix cinnamon into the cake batter - need more than on the ingredient list.