Preheat oven to 350 degrees. Use a 9x5-inch loaf pan and spray with non-stick spray or line with foil and spray with non-stick spray to get out easily for slicing.
Mix brown sugar and cinnamon together in a bowl. Set aside.
In another medium-sized bowl, beat white sugar and butter together using an electric mixer until smooth and creamy.
Beat in eggs, 1 at a time, until blended in; add in vanilla extract.
Combine & whisk flour and baking powder together in another bowl then gradually into creamed butter mixture and mix until just combined.
Mix buttermilk into batter until just combined. Add blueberries and fold in.
Pour half the batter into the prepared loaf pan; and then sprinkle half the brown sugar/cinnamon mixture on top of batter spreading it out
Pour the remaining cake loaf batter over the cinnamon/sugar and repeat sprinkling with the remainder of the sugar/cinnamon mixture on top.
Bake in the preheated oven until a toothpick inserted in the center of the loaf comes out clean, approximately 50-60 minutes.
To make glaze, mix powdered sugar and milk or cream together until well mixed.
Let cool for about 15 minutes before drizzling with glaze if you want it to soak in. You can also drizzle with glaze after it's cooled.