Preheat oven to 350 degrees F (reduce temperature to 325 degrees F if your pan is dark/non-stick). Grease and flour a 10-cup Bundt pan; set aside.
In a medium bowl, whisk together 2½ cups of the all-purpose flour, the baking powder and salt; set aside.
In the bowl of a stand mixer (or large mixing bowl), use your fingertips to rub together the sugar and lemon zest until the zest is completely incorporated and the sugar is evenly moistened. Add the butter and cream together on medium speed until light and fluffy, 3 to 5 minutes.
Reduce the speed to low and add the eggs one at a time, mixing for a minute after each and scraping down the bowl before adding the next. Add the vanilla and mix briefly to combine.
With the mixer still on low, add 1/3 of the flour mixture, beating until just barely combined, followed by ½ the buttermilk, another 1/3 of the flour mixture, the remaining buttermilk and the remaining flour.
In a large bowl, combine the blueberries and the remaining 2 tablespoon of all-purpose flour, tossing together so they are evenly coated. Use a rubber spatula to gently fold the blueberries into the cake batter. Spread the cake batter in the prepared pan and smooth the top. Bake for 55 to 60 minutes, until a cake tester comes out clean. Cool the cake on a wire rack for 30 minutes, then turn it out onto a serving platter and let cool completely.
Once the cake is cool, whisk together the powdered sugar, milk and butter until smooth. The icing should be quite thick (if you'd like it thinner, you can add more milk, a teaspoon at a time, until you get it to the consistency you want). Use an offset spatula to spread the glaze on top of the cake, giving it a little nudge down every so often. The cake can be stored, covered, at room temperature for up to 4 days.