Preheat oven to 350 degrees F. Spray a 9x5 loaf pan with nonstick spray and set aside.
For the blueberry compote: add blueberries and sugar to a small saucepan over medium heat. Bring to a simmer. Mash blueberries as you're stirring. You want some chunks but some smoothness too Continue cooking until mixture has reduced to 3/4 cup, about 10 minutes. Set aside to cool slighty.
Add whole milk and lemon juice to a large bowl. Let sit for 5 minutes. Whisk in eggs, sour cream, oil, vanilla extract and sugar. Add flour, baking powder and salt and fold in until just combined. Set aside.
In a small bowl, combine the coarse sugar and lemon zest. Roll between your fingers as you're mixing to release the oils from the lemon zest.
Pour half the batter into the prepared loaf pan. Dollop 6 tablespoons of the blueberry compote randomly over the batter. Swirl with a toothpick. Gently spread the remaining batter over the blueberries. Dollop the remaining compote over top and swirl with toothpick. Sprinkle with lemon sugar. Bake for 50 to 60 minutes, until a toothpick comes out clean.