• Preheat the oven to 375℉/190℃. Line the muffin tin with muffin liners and set aside. Melt the butter and allow it to cool as you prep the rest of the ingredients. Chop the rhubarb and strawberries into small pieces, about 1/4" thick and set aside to use later.
  1/4 cup unsalted butter, 1 cup fresh strawberries, 1 cup fresh rhubarb

For the streusel

• In a medium-sized bowl, add in flour, cold butter, and white sugar. With your hands, mix it together until a crumbly streusel forms. Set in the refridgerator to chill as you make the muffin batter.
  3/4 cups all-purpose flour, 1/3 cup white sugar, 5 tbsp butter

For the muffin batter

• In a large bowl, mix together the dry ingredients; flour, cornstarch, baking soda, and baking powder, and set aside.
  2 1/4 cups all-purpose flour, 2 tsps cornstarch, 1 tsp baking soda, 2 1/4 tsp baking powder
• In another large bowl, add the wet ingredients; white sugar, eggs, vanilla, and sour cream. . Whisk together for 2-3 minutes until smooth.
  1/4 cup oil, 2 large eggs, 1 tbsp vanilla, 1 cup sour cream, 1 cup white sugar
• Add the dry and wet ingredients together and mix together until almost combined.
• In the bowl with the strawberries and rhubarb, sprinkle 1 tbsp of flour on top and mix around to evenly coat them in the flour. This will help prevent them from sinking as they bake.
• Mix the strawberries and rhubarb into the bowl until evenly distributed and there are no more flour streaks.
• Scoop the batter evenly between the muffin liners. Sprinkle a handful of streusel on top.
• Bake the muffins for 25-30 minutes. They are ready when a toothpick inserted in the middle comes out clean.
• Allow the muffins to cool, and enjoy! They are so delicious and best served within the first few days. You can also store them in an airtight container for up to one week in the refrigerator.