Preheat oven to 350 degrees. Grease a 9 x 9 baking pan with cooking spray and line with parchment; set aside.
In a large bowl, use a handheld mixer to cream together the butter and brown sugar until light in color, about 2 minutes. Add in the ricotta and cream for 4-5 minutues, or until lightened in color. Beat in the eggs, one at at time, then add in the vanilla, lemon zest, and lemon juice. Don't worry if the mixture looks curdled.
In a separate bowl, whisk together the flour, baking powder, baking soda, and salt. Add to the wet mixture and beat until just combined. Fold in the blueberry mixture and pour the batter into the prepared pan; set aside.
For the streusel topping, in a bowl stir together the brown sugar and oats. Stir in the butter until mixture resembles a coarse crumble. Use you hands to sprinkle the streusel over the blueberry batter in the pan.
Bake on the middle shelf in the oven for 50-55 minutes, or until a toothpick inserted in the center comes out clean. Let cool on a wire rack before cutting.
This is a great make ahead option. Just refrigerate in an airtight container for up to a week or freeze for up to a month.
Recipe courtesy of This Delicious House. Sign up for more recipes today at https://thisdelicioushouse.com