• Preheat the oven to 425℉. Line your muffin tin with 12 liners and set aside. Melt the butter and prepare to measure the rest of your ingredients as it cools.
  1/3 cup unsalted butter

For the streusel

• In a small bowl, make the streusel. Combine flour, white sugar, and cold cut up butter. Using your hands, mix it together until combined into a crumbly, streusel mixture. Set aside while you make the muffin batter.
  5 tbsp unsalted butter, 1/3 cup white sugar, 3/4 cup all-purpose flour

For the muffins

• In a medium-sized bowl, add the flour, baking powder, baking soda, cornstarch, and salt. Mix together and set aside.
  2 1/2 cups all-purpose flour, 3 tsp baking powder, 1 tsp baking soda, 1/2 tsp salt, 1 tbsp cornstarch
• In a large bowl (this is the bowl you'll be using for the entire bake so make sure it is large!), add the white sugar and lemon zest. Using your fingers, rub them together for 2 minutes. This is going to release the lemon oils and fragrance.
  1 cup white sugar, zest of 1 large lemon
• Add in lemon juice, oil, butter, buttermilk, eggs, and vanilla. Whisk until well combined. It's okay if it is clumpy.
  1/3 cup unsalted butter, 1/4 cup oil, 2 large eggs, 3 tbsp lemon juice, 1 cup buttermilk*, 2 tsp vanilla
• Add in the dry ingredients and using a spatula, slowly fold until a soft muffin batter forms. Mix until JUST combined.
• In the bowl with the blueberries, add 1-2 tsps of flour and gently toss around until evenly coated. The light coating of flour will absorb any extra liquid it may have before adding it into the mixing bowl.
  1 1/2 cups fresh blueberries*
• Add the blueberries and mix in a few times.
• Evenly divide the batter between the muffin liners.
• Sprinkle streusel on top.
• Bake the muffins at 425°F for 5 minutes, then turn down to 350°F and bake for an additional 15-17 minutes. The muffins are ready when a toothpick inserted comes out clean.
• Enjoy!!