Preheat oven at 350ºF (180ºC).
Butter or spray an 8x3-inch (20x7cm) loaf cake pan. I recommend you line it with parchment paper for easier removal. See Notes below for options.
In a large bowl mix dry ingredients: sifted 2 cups all-purpose flour, 1 tablespoon baking powder and 1 teaspoon salt. Add 1 cup sugar and stir to combine.
In another bowl stir together 2 eggs, ¾ cup whole milk, ¼ cup vegetable oil, 1 teaspoon vanilla extract, lukewarm 4 tablespoons unsalted butter and 2 teaspoons orange zest. Do not beat but mix well until no streaks of egg whites remain.
Add all of the wet ingredients at once to the dry ingredients.
Mix until you barely have streaks of flour, but do not overmix. It will be lumpy and not completely mixed. It's key that you don't overmix!
Add 1 ½ cups blackberries and fold in lightly, trying not to crush them.
Pour into the prepared pan, smooth the top and bake for 30-40 minutes, until the top is cracked and golden and a tester inserted in the center comes out clean.
Let cool on a wire rack for 20 to 30 minutes and carefully remove. Let cool completely.
You can glaze it, but I find it’s amazing plain. Your call.
Keep wrapped in film.