Preheat the oven to 350ºF (180°C).
Line 12 regular muffin tins with paper liners or butter/spray the pans. The yield can vary depending on the size of the berries.
In a large bowl, sift the dry ingredients: 2 cups all-purpose or cake flour, 2 teaspoons baking powder and ½ teaspoon salt. Add 1 cup white granulated sugar and stir to combine.
In a medium bowl, combine 2 eggs, ¾ cup milk, ¼ cup vegetable oil, 4 tablespoons unsalted butter, lukewarm and ½ teaspoon vanilla extract. Do not beat, but stir well until no streaks of egg whites remain.
Add 1 tablespoon orange or lemon zest.
Add the mixed wet ingredients at once to the bowl with the dry ingredients. Stir until you barely have streaks of flour, but do not overmix. It will be lumpy and not completely mixed, and that is fine.
Add 1 ½ cups blackberries and stir lightly, being careful not to mash them. I do it with a rubber spatula.
Divide the mixture evenly among the muffin cups or muffin liners. For a crunchier topping, you can add a sprinkling of sugar (half a teaspoon) to each muffin top before baking.
Bake for 25 minutes, until the top is cracked, golden brown, and a cake tester or toothpick inserted in the center comes out clean. Don't overbake.
Let cool on a wire rack and eat warm or let cool down completely.
They are best eaten the day they are made, but you can keep them for a day at room temperature covered or wrapped.
Store leftovers, covered in plastic wrap or in an airtight container, in the refrigerator for a few days or in the freezer for a month.