In a large bowl, whisk together flour, baking powder, baking soda, and salt.

In another bowl, mix melted butter, oil, and sugar until smooth.

Add eggs and egg yolk, mixing well. Stir in buttermilk, vanilla, and lemon zest.

Combine wet and dry ingredients until just mixed. Do not overmix.

Toss blueberries with 1 tablespoon flour and gently fold into batter.

Let batter rest for 15–20 minutes.

Divide batter evenly into 12 jumbo muffin cups, filling almost to the top.

In a small bowl, mix crumb topping ingredients until crumbly.

Generously sprinkle crumb topping over each muffin.

Bake at 425°F for 5–7 minutes, then reduce heat to 350°F.

Continue baking for 18–22 minutes, or until tops are golden and a toothpick comes out clean.

Let cool slightly before serving.