Preheat oven to 350ยบ.
Mix sourdough discard, lemon juice, melted butter, eggs, sour cream, milk, and vanilla extract well.
Add in all dry ingredients and blueberries.
Stir until combined, but do not over mix.
Fill greased muffin tins with mixture.
Mix crumble topping.
Add heaping spoonful of crumble topping to each muffin until all topping is used.
Bake 30-40 minutes. My oven takes closer to 40 minutes.