Preheat the oven to 425 and prepare a muffin pan with liners.
In a large mixing bowl cream together the sugar and room temperature butter.
Add eggs, vanilla, sourdough discard, sour cream, and lemon zest.
Once combined, add dry ingredients: flour (reserve about 2 Tablespoons to mix in with the blueberries), baking powder, baking soda, and salt to the wet ingredients. Mix just until flour mixture is incorporated into wet ingredients.
Coat blueberries with the reserved flour and then fold them gently into the batter.
Sprinkle crumb topping on top of muffins.
Bake in preheated oven for 5 minutes. Then reduce heat to 350 and cook for an additional 18-20 minutes or until the toothpick comes out clean.