• Preheat oven to 375°. Lightly grease a 9 inch square baking pan.

For the cake

• With a mixer, cream the butter and sugar until light and fluffy. Beat in the egg, buttermilk, vanilla, baking powder and salt. Mix until combined- batter may curdle a bit, this is o.k.
• Stir in half the flour until combined, then stir in the remaining half. Batter will be thick. Gently fold in the blueberries. Spread the batter evenly into prepared pan. Set aside.

For the crumb topping

• Combine the flour, brown sugar, cinnamon and salt in a bowl. Add in butter and mix with fingers or pastry blender until crumbly. I use my fingers and just keep tossing the butter with the dry ingredients and pressing them together to form a very coarse crumb mixture. Spread this evenly on top of the batter.
• Bake cake in preheated oven about 45 to 50 minutes or until a toothpick comes out clean in the center. Cool completely on a wire rack.

For the glaze

• While the cake is cooling, whisk all the glaze ingredients together in small bowl until smooth. Add additional lemon juice to get the consistency you want for drizzling on the cake. Once the cake is cooled, either drizzle then cut to serve, or cut into pieces then drizzle with glaze.