In a small bowl, combine flour, brown sugar, cinnamon, oats and salt. Cut in butter with a fork until mixture is in a crumbly state. Set aside.
Whisk powdered sugar, vanilla and milk in a small bowl until smooth. Set aside.
Preheat oven to 350 degrees. Prepare a 9 inch springform pan with cooking spray on sides and parchment paper on the bottom.
Add the flour and baking powder to a medium size mixing bowl, mix together well and set aside.
Cream sugar and butter together in large mixing bowl bowl using an electric mixer.
Add the egg and mix until well combined.
Mix in the sour cream, milk and vanilla extract.
Add your flour/baking powder mixture to your wet ingredients, mix well and then gently stir in blueberries.
Pour your batter into your springform pan and top with your streusel mixture.
Bake at 350 degrees for 45-50 minutes until a toothpick inserted into the middle comes out clean.
Cool for 15-20 minutes, remove from springform pan and drizzle glaze over top of coffee cake.
If you prefer you can add the blueberries to the top of the coffee cake prior to adding the streusel mixture instead of folding them into the batter. Or go all wild and crazy and add 1/2 to the batter and 1/2 to the top.