Blueberry (Boo-baby) Muffins

These were, hands-down, the best blueberry muffins I've ever had. I made them a second time a week after the first, only I substituted plumcots for the blueberries. I had never cooked with plumcots before, but they sounded good and were on sale. The muffins turned out fantastic with them, also. In fact, Jamie said he thought he even liked the plumcot version better! Next up, I'm trying them with blackberries! (*Update - they're delicious with blackberries, too!)

Blueberry Muffins

Topping:
1/3 cup sugar (I used turbinado sugar, which is a bit crunchier)
1 1/2 tsp lemon zest (I didn't have any lemons, so left this out)
(Stir these together for the topping)

Muffins:
2 cups (about 10 oz) fresh blueberries
1 1/8 cups plus 1 tsp sugar
2 1/2 cups flour
2 1/2 tsp baking powder
1 tsp salt
2 eggs
4 Tbsp unsalted butter, melted and cooled slightly
1/4 cup vegetable oil
1 cup buttermilk (or 3/4 cup plain yogurt mixed with 1/4 cup milk)
1 1/2 tsp vanilla

-Adjust oven rack to upper-middle position and preheat to 425 degrees. Generously spray a muffin tin with cooking spray.
-Bring 1 cup of berries and 1 tsp sugar to a simmer in a small saucepan over medium heat. Cook, mashing berries with a spoon and stirring frequently, 6-10 minutes, until the berries have broken down and the mixture is thickened and reduced. Transfer to a small bowl and let cool to room temperature (10-15 minutes.) (*you could do this step a day before.)
-Whisk flour, baking powder, and salt together in a large bowl.
-In a medium bowl, whisk remaining 1 1/8 cup sugar together with eggs until thick, about 45 seconds. Slowly whisk in the butter and oil until combined. Whisk in the buttermilk and vanilla until combined.
-Fold the egg mixture and remaining cup of blueberries into the flour mixture just until moistened - do not overmix.
-Divide the batter equally among prepared muffin cups (they will be very full.) Spoon a teaspoon of the cooked berry mixture into the center of each mound of matter. Using a chopstick, swirl the mixture gently. Sprinkle topping on each muffin.
-Bake until golden and firm, 17-19 minutes, rotating muffin tin once during baking. Cool muffins in the tin 5-7 minutes, then turn onto a wire rack and cool at least 5 minutes before serving.