01 -
Preheat the oven to 350°F (175°C) and spray an 8-1/2 x 4-1/2 inch loaf pan with cooking spray or line with parchment paper.
02 -
In a small bowl, whisk together the flour, baking powder, and salt to distribute ingredients evenly and remove any lumps.
03 -
Place sugar and lemon zest in a mixing bowl. Rub between your fingers to infuse the sugar with lemon oils. Add sour cream, eggs, vanilla, and lemon oil, then whisk until well blended.
04 -
Using a silicone spatula, fold in half of the dry ingredients until well blended. Then fold in the remaining flour mixture.
05 -
Gradually pour the vegetable oil into the batter while stirring continuously with a silicone spatula until fully incorporated.
06 -
Transfer 1/2 cup of the batter to a small bowl and stir in the blackberry jam and blue food coloring (if using).
07 -
Gently fold the flour-coated blackberries into the remaining batter in the larger bowl.
08 -
Pour about 2/3 of the blackberry batter into the prepared loaf pan. Then pour the jam-infused batter on top, followed by the remaining blackberry batter.
09 -
Bake for 55 to 65 minutes, or until the loaf starts pulling away from the pan's edges and a toothpick inserted in the center comes out clean or with a few crumbs attached.
10 -
Allow the loaf to cool in the pan for 5 to 10 minutes. Run a knife around the edges and remove from the pan. Cool completely on a wire rack.
11 -
In a bowl, combine powdered sugar and salt. Pour in 2 tablespoons of lemon juice and whisk until smooth. Add more lemon juice gradually if a thinner consistency is desired.
12 -
Drizzle the glaze over the completely cooled loaf. Allow to sit at room temperature for about 10 minutes until the glaze sets.