The cake has a delicious buttery flavor, a soft and tender crumb and it's brimming with fresh, sweet, juicy blueberries. Then it's covered with a delicate yet perfectly crisp, cinnamony crumble that will make your heart sing. This is a cake you don't want to miss out on!
Add flour, sugar, cinnamon and salt to a food processor and pulse several times.
Add in butter and pulse until mixture appears sandy with tiny bits of butter. Transfer to refrigerator and chill while preparing cake.
For the cake:
Butter a 9 by 9-inch baking dish. Line with parchment paper and butter parchment paper, set aside.
In a mixing bowl whisk together flour, baking powder and salt, set aside.
In the bowl of an electric stand mixer fitted with the paddle attachment cream butter and granulated sugar until pale and fluffy. Mix in egg and vanilla.
Remove bowl from stand mixer (scrape excess butter on paddle into bowl).
Add 1/2 of the flour mixture (to sugar/egg mixture) and fold just nearly until combined then add in 1/2 of the milk and fold just until nearly combined, repeat process with flour and milk once more, then add in blueberries and fold just to evenly distribute.
Pour batter into prepared pan and spread into an even layer. Remove crumble from refrigerator and sprinkle evenly over top.
Bake in preheated oven until toothpick inserted into center comes out clean (center also shouldn't fall when lightly pressed), about 30 - 35 minutes.
Let cool at least 5 minutes then lift from pan using parchment. Cut into squares and serve warm. Store in an airtight container.
Notes
*If using frozen blueberries, you'd want to fold them into the batter frozen (do not thaw), and you'll likely need to add 10 or so minutes to the bake time.