Prep your pan and oven. Heat the oven to 400°F (200°C). Line a 12-cup muffin tin with paper liners or grease the cups well. A hot oven helps the muffins rise tall.

Mix the dry ingredients. In a large bowl, whisk the flour, sugar, baking powder, baking soda, and salt. Set aside a tablespoon of this mixture to toss with the blueberries.

Whisk the wet ingredients. In a separate bowl, whisk the buttermilk, eggs, melted butter, oil, vanilla, and lemon zest until smooth. Make sure the butter isn’t hot, or it can scramble the eggs.

Combine gently. Pour the wet ingredients into the dry. Stir with a spatula until just combined. The batter should be thick and a little lumpy. Do not overmix; that’s how you keep muffins tender.

Fold in the berries. Toss the blueberries with the reserved tablespoon of flour (this helps them stay suspended). Gently fold them into the batter so they’re evenly distributed.

Fill the cups. Divide the batter between the 12 muffin cups, filling them almost to the top for a bakery-style dome. Sprinkle the tops with coarse sugar, if using.

Bake. Bake for 16–20 minutes, until the muffins are golden and a toothpick comes out with a few moist crumbs. If using frozen berries, add a minute or two to the bake time.

Cool. Let the muffins sit in the tin for 5 minutes, then transfer them to a wire rack. They firm up as they cool, but they’re wonderful slightly warm.