1 and 1/4cupfresh blueberries, if using frozen berries do not thaw first
For the Vanilla Glaze
Make the Streusel
In a medium-sized bowl whisk together the flour, sugars and cinnamon. Then stir in the melted butter with a spatula or spoon. The mixture should look like wet sand and crumble if you squeeze it in your palm. Set aside.
Make the Cake
Preheat the oven to 350F degrees. Grease and lightly flour the bottom and sides of a 9 inch springform pan.
In a medium-sized bowl whisk together the flour, baking powder, baking soda and salt. In a separate large bowl using an electric mixer on medium speed, beat the butter and sugar together until fluffy. Then add in the eggs and vanilla and continue mixing until evenly combined. Then turn the mixer down to low speed and beat in the sour cream, followed by the flour mixture. Scrape down the sides of the bowl as necessary, then carefully beat in the buttermilk. Be careful not to overmix the batter.
In a medium bowl, toss the blueberries with 2 teaspoons of flour. Then gently stir into the cake batter using a large wooden spoon or rubber spatula.
Pour/ spoon the batter into the prepared pan, then crumble the streusel mixture over top. Bake in the preheated oven for 45-55 minutes or until an inserted toothpick comes out clean or with a few cake crumbs, or when you give the pan a gentle nudge the cake doesn't wobble. If you notice the top starting to get brown around 40 minutes, you can tent a piece of tin foil and place it over top.
Allow to cool fully in the pan.
Make the Glaze and Serve
In a small bowl, whisk together the powdered sugar and milk. Add a little extra milk or powdered sugar as needed.
Once the cake is fully cool, trace around the sides of the pan with a thin knife then unclamp the springform pan. Cut into slices, and drizzle each piece with the glaze.
*Ensure these ingredients are room temperature before getting started. **If you don't have buttermilk, add 1 teaspoon of distilled vinegar to 1/3 cup of milk and allow to sour for 5 minutes before using.Leftovers can be stored in an airtight container at room temperature for 2 days, or in an airtight container in the fridge for up to 4 days.