Combine all of the ingredients for the streusel topping except for the butter in the bowl of your mixer. Mix on low until combined. Add butter and mix until contents resemble wet sand, approximately 3 to 4 minutes.
Preheat the oven to 350°F. Use soft butter to coat the inside of a 9" cake pan or springform pan and then add 1 tablespoon of flour to dust the inside. Set aside.
In a medium-sized mixing bowl combine flour and baking powder.
In the bowl of your electric stand mixer fitted with the paddle attachment, beat the butter, sugar, salt, and zest on medium until light and fluffy, about 3 minutes.
Beat in vanilla, about 30 seconds.
Add eggs one at a time until incorporated. The batter will appear "broken".
On a low speed add four in 2 to 3 increments add the flour beating between each addition until incorporated. Scrape down the sides and beat until all flour is combined.
Fold the blueberries in by hand using a spatula, trying not to break the berries. The batter will be thick.
Add the batter to the prepared pan and spread evenly.
Take streusel and make approximately marble-sized clumps with your fist and sprinkle on top of batter.
Bake until the cake is golden brown and a toothpick comes out clean, about 50-55 minutes.
Transfer to a wire rack and let cook at least 20 minutes before serving.
This recipe was adapted by West Via Midwest https://www.westviamidwest.com/blueberry-buckle-recipe/The butter in the original recipe is 10 tablespoons. I used 6. The texture and flavor was amazing.
This recipe was calculated using the exact brands and measurements I used to make this recipe. If you are following a strict diet please note changing anything will cause the nutritional info to change. My calculations are intended as a guide only.