Preheat the oven to 350°F.
Butter and flour a 9 inch by 5 inch loaf pan.
1¾ cup (227grams or 8 ounces) bleached all-purpose flour, 1 stick (113 grams or 4 ounces) unsalted butter, softened
Sift together the dry ingredients (flour, baking powder, baking soda, salt) into a medium sized bowl.
1¾ cup (227grams or 8 ounces) bleached all-purpose flour, ½ teaspoon baking powder, ½ teaspoon baking soda, ½ teaspoon salt
Cream the butter, sugar, and lemon zest together until light and fluffy. If using a stand mixer, this will take about 5 minutes on medium speed, longer if using a hand mixer.
1 stick (113 grams or 4 ounces) unsalted butter, softened, 1 cup (200 grams or 7.1 ounces) granulated sugar, zest of 3 lemons (about 2 tablespoons)
Add the eggs one at a time, beating for a minute after each addition and scraping down the bowl as necessary.
2 large eggs
Add approximately one half of the dry ingredients and mix on low speed until they are just incorporated.
Add the buttermilk and lemon juice and beat until mixed. Scrape down the bowl.
½ cup buttermilk, ¼ cup lemon juice
Add the remaining dry ingredients and mix until just barely incorporated.
Toss the blackberries in a small bowl with the extra 1 tablespoon of flour and then add the berries to the batter. Using a spatula, gently fold in the berries by hand.
1 cup blackberries, washed, dried, and halved if large
Pour the batter into the prepared pan, even out the batter and give the pan a few thwacks on the counter to remove any air bubbles.
Bake the blackberry lemon batter for 50 to 60 minutes until the top has started to brown and a toothpick inserted into the center comes out clean. If the top is browning too quickly, cover it lightly with foil.
Cool in the pan for 10 minutes, and then invert and transfer to a cooling rack.