Preheat oven to 425°F. Spray a 6-cup jumbo-size muffin tray with baking spray or line with paper liners. Set aside.
In a large bowl, whisk together the flour, sugar, baking powder, baking soda and salt. Add chocolate chips and stir to evenly distribute.
3 cups (375g) all-purpose flour, 1 cup (200g) granulated sugar, 1 Tablespoon baking powder, 1/2 teaspoon baking soda, 1/2 teaspoon salt, 2 cups semisweet chocolate chips
In a separate bowl, combine the eggs, buttermilk, melted butter, oil, and vanilla. Whisk well, then add to the flour mixture, stirring by hand with a wooden spoon or rubber spatula just until combined. It's okay if the batter is lumpy and thick. Do not overmix.
2 large eggs, 1 cup (240ml) buttermilk or milk, 1/4 cup salted butter, 1/4 cup vegetable oil, 2 teaspoons vanilla extract
Divide the batter between the muffin cups, filling them to the top. Sprinkle with coarse sugar. Bake at 425°F for 5 minutes, then decrease the oven temperature to 350°F without opening the oven door and continue to bake for 24-26 minutes until a toothpick inserted into the center of a muffin comes out clean. Do not overbake.
Coarse sugar
Cool for 5-10 minutes in the pan, then turn out onto a wire cooling rack.