• Preheat the oven to 375℉/190℃. Line a muffin tin with liners and set aside.

For the streusel

• In a bowl, add the butter, flour, sugar, and lemon zest. With your fingers or a fork, combine until a buttery streusel forms. Place in the refrigerator as you make the muffin batter.
  1/4 cup white sugar, 4 tbsp unsalted butter, 1/2 tsp lemon zest, 2/3 cups all-purpose flour

For the muffin batter

• In a bowl, add the flour, cornstarch, baking soda, baking powder, and salt. Stir to combine and set aside.
  2 cups all-purpose flour, 1 tbsp cornstarch, 1 tsp baking soda, 2 tsp baking powder, 1/4 tsp salt
• In another large bowl, add the lemon zest and white sugar. Using your fingers, rub them together to combine for about a minute. The aroma of lemon will fill the air.
  1 cup white sugar, Zest from 2 large lemons, or 3 medium
• Into the same bowl with the lemon sugar mixture, add eggs, vanilla, lemon juice, oil, and yogurt. Whisk to combine for another one or two minutes.
  2/3 cups oil, 3/4 cups plain yogurt, 1/4 cup lemon juice, 2 large eggs, 1 tsp vanilla
• Add the dry ingredients in and mix just until a soft muffin batter forms. Do not over-mix!
• Divide the batter evenly between the liners, filling them up to the top. Add a handful of streusel on top of each muffin.
• Bake for 22-28 minutes or until a toothpick inserted comes out clean. Allow to cool, and enjoy!