STREUSEL

1. With a fork, mix together the flour, sugar, cinnamon and salt in a small bowl.
2. Add in the melted butter and vanilla extract. Mix well and set aside.

LEMON CAKE

1. Preheat oven to 350°F (180°C).
2. Lightly grease the bottom and sides of the 8x8 inch pan with softened butter. Line the whole pan (bottom and sides) with parchment paper and set aside.
3. In a food processor, pulse the granulated sugar and the zest from two lemons. Set aside.
4. In a small bowl, combine the milk, sour cream, and lemon juice. Set aside for at least 10 minutes.
5. In a medium bowl, combine the flour, salt and baking powder. Set aside.
6. In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter and lemon sugar until light and fluffy.
7. Add the eggs and one egg yolk, one at a time, blending well after each addition. Add the vanilla extract and mix until incorporated.
8. Add ⅓ of the flour mixture to the creamed butter and sugar. Beat on low until incorporated. Next, add ⅓ of the milk mixture and blend until smooth. Do this alternation two more times. Don't overmix!
9. Pour the batter into the prepared pan and spread evenly. Set aside.

BLUEBERRY TOPPING

1. Toss the blueberries with the lemon juice, then add the granulated sugar and all-purpose flour until coated. Do not overmix!
2. Scatter the blueberries on top of the prepared batter. Then toss the crumble topping over the batter, leaving some in large clumps.
3. Bake for 50-60 minutes or until the top is lightly browned and a toothpick inserted in the center comes out with moist crumbs attached.
4. Cool for 15 minutes in the pan. Remove the cake from the pan then cool for at least another 10 minutes before cutting to serve.
5. Serve warm with a scoop of vanilla ice cream (optional)!