Preheat the oven to 350 degrees.Butter and flour a 10-cup bundt pan.Whisk flour, baking powder, and salt together.With an electric mixer, beat together sugar and butter until fluffy.Continue beating, adding eggs, one at a time.Add vanilla and zest, and mix well.Gradually add in dry ingredients alternating with buttermilk, ending with flour mixture.Turn off the mixer and gently fold in blueberries.Pour batter into a bundt pan.Bake until a cake tester or wooden skewer comes out clean about 50 minutes to an hour.Cool cake on a rack for 15 minutes.Turn the cake onto a cake plate and cool completely before frosting.Sour Cream Icing: Using a hand mixer, cream butter, sour cream, vanilla, and lemon juice until smooth.Gradually add confectioners sugar.Add salt and mix until smooth.Pour icing around the top of the cake allowing it to run down the sides.