Preheat oven to 375 degrees. Prepare two 12-cup muffin tins with cooking spray.
Mix the flour, sugar, baking powder, baking soda and salt together in a large bowl.
Whisk the sour cream, milk, eggs and vanilla together in a separate bowl.
Mix the wet ingredients with the dry ingredients and stir gently to combine. Add the melted butter and stir well.
Fold in strawberries and rhubarb.
Fill each muffin cup ¾ full. Bake until golden brown, 25-30 minutes.
Let cool in pan 5 minutes, then remove to wire rack. Shortly before serving, top with glaze.
For glaze:
Combine powdered sugar and basil syrup in a small bowl.