For the cake

• Preheat the oven to 350°F. Grease a 9-by-5-inch loaf pan with oil and set aside.
• Add the granulated sugar and lemon zest to a large bowl and, using clean hands, rub the zest into the sugar to release the oils and flavors. Whisk in the sour cream, eggs, ½ cup oil, 2 tablespoons of the lemon juice, and food coloring (if using) until smooth.
• In a medium bowl, whisk together the baking powder, baking soda, salt, and 2 cups of the flour. In another medium bowl, toss the blueberries with the remaining 1 tablespoon flour and set aside. Fold the flour mixture into the egg mixture until just combined. Fold in the blueberries.
• Transfer the batter to the prepared loaf pan, smoothing the top with a spoon or small offset spatula. Bake until golden and a toothpick inserted in the center comes out clean, 1 hour to 1 hour 10 minutes, covering with foil to prevent excess browning after 40 minutes.
• Let cool in the pan for 10 minutes then place a wire cooling rack over the pan and flip to remove the bread. Place the bread right-side up and let cool completely, about 1 hour.
• Meanwhile, in a medium bowl, stir together the powdered sugar, butter, and remaining 3 tablespoons lemon juice. Add water, 1 teaspoon at a time, until a thick, but pourable consistency is achieved.
• Pour the glaze over the cooled loaf, allowing it to drip down all sides. Let sit for 30 minutes to set before slicing and serving.