Preheat the oven to 425 degrees. Line a muffin pan with liners or spray with a nonstick baking spray.

To make topping, use a fork to mix together the 1/4 cup of sugar and the lemon zest. Set aside.

In a medium-sized pot, bring one cup of the blueberries and one teaspoon of sugar to a boil. Cook over medium heat until the berries begin to break down, and mash with a fork until the mixture begins to thicken, about four to five minutes. Transfer to a bowl and set aside to cook for about 10 minutes.

In a large bowl, whisk together flour, baking powder and salt. In a medium bowl, whisk together remaining sugar and eggs until they are thick and homogenous. Mix in butter and oil and then mix in buttermilk and vanilla. Add to flour mixture, along with remaining blueberries and fold together. Batter will be slightly lumpy…do not overmix.

Using an ice cream scoop or large spoon, fill muffin cups. The batter will fill the entire cup. Top each muffin with about a teaspoon of the cooked berries and swirl into batter with a toothpick or a knife.

Top with lemon sugar mixture and bake at 425 degrees for 17-19 minutes, rotating pan half way through baking time. Cool in tin for five minutes before transferring to wire rack to cool completely.