Make Crumble
Whisk together flour, sugars, cinnamon, and salt.
Pour in melted butter and mix until clumps form.
Chill.
Prepare Blueberries
Toss blueberries with zest.
Toss with cornstarch.
Make Batter
Whisk together flour, baking powder, baking soda, and salt.
Cream butter and sugar.
Mix in egg and extracts.
Mix in sour cream.
Bake Cake
Mix dry ingredients into batter until almost combined.
Fold in ½ of the blueberries.
Spread batter into prepared pan.
Top with remaining blueberries.
Top with crumble.
Bake at 350F for 45-50 minutes.
Cool 1 hour.
Make Icing
Whisk together icing ingredients.
Drizzle over cooled cake.
