Preheat the oven to 350°F (175°C). Grease a 9-inch round cake pan and line the bottom with parchment paper.
In a small bowl, toss the blueberries with lemon juice and lemon zest; set aside.
In another bowl, whisk together 1 ½ cups flour, baking powder, baking soda, and salt.
In a large mixing bowl, cream the softened butter and granulated sugar until light and fluffy.
Add the eggs one at a time, mixing well after each addition.
Stir in the vanilla extract, sour cream, and milk until combined.
Gradually add the dry ingredients to the wet mixture, mixing until just combined.
Gently fold in the blueberries.
Pour the batter into the prepared cake pan.
In a separate bowl, prepare the crumble topping by combining ½ cup flour, rolled oats, brown sugar, melted butter, and cinnamon until crumbly.
Sprinkle the crumble evenly over the cake batter.
Bake for 40-45 minutes or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.