In a bowl combine topping dry ingredients (sugar, cinnamon, flour).
Cut in the butter with a pastry cutter or 2 knives until dry ingredients have combined well with the butter. If the butter is soft, you can use your fingers. There should be little clumps without a lot of extra loose flour mixture.
Refrigerate topping while you make the batter.
Using a stand-mixer, combine sugar and shortening until well blended (3-5 minutes).
Add in egg and mix until combined.
Add milk and vanilla extract. Mix again.
Sift dry ingredients together in a separate bowl.
Gradually mix dry ingredients into wet ingredients.
Remove bowl from mixer. Gently fold in the blueberries with a spoon (try not to let the berries burst). The batter will be very thick.
Put in a greased 8x8 or 9x9 inch baking pan and press batter out to the corners of the pan.
Remove topping from refrigerator and sprinkle evenly over top of the cake batter.
Bake for 45-50 minutes or until toothpick inserted in center comes out clean.
While cake is cooling on a wire rack, mix up the ingredients for a glaze, adding milk 1Tbsp at a time until it reaches the desired consistency. If it gets too wet and runny, add more sugar. Cover glaze until cake cools.
After cake has cooled completely, use a spoon and drizzle the glaze over top of the cake.