Preheat oven to 350ºF (177ºC) and prepare parchment-lined or buttered 8-inch baking dish.
In a medium-sized mixing bowl, stir together flour, baking powder and salt. Gently fold blueberries into flour mixture just until they’re flour-covered and well distributed. Set aside.
In a large bowl, add sugar and lemon zest and press together until the zest is fully absorbed into the sugar and the sugar is yellow and fragrant. Add butter and cream together. Whisk in egg and vanilla.
Fold 1/3 of the berry and flour mixture into the wet ingredients. Pour in buttermilk and continue to stir until well combined. Stir in remaining flour and berries and mix just until the batter is nice and thick, and the berries are evenly distributed.
Spread batter into prepared pan and sprinkle the teaspoon of sugar across the top. Bake for 40 minutes until golden and a tester comes out clean.
Remove from oven and let cool on a wire cooling rack for at least 20 minutes before slicing.