1 c. unsalted butter (room temperature) plus more (for baking pan)
2 c. granulated sugar
4 large eggs (room temperature)
3 c. all-purpose flour
1/2 tsp. baking soda
1 c. fresh blueberries
1 c. buttermilk
2 1/2 tbsp. fresh grated lemon zest (3 large lemons)
2 1/2 tbsp. fresh squeezed lemon juice (2 lemons)

For The Glaze:

1/2 c. confectioners sugar
1/2 c. freshly squeezed lemon juice (4 lemons)
3 tbsp. freshly grated lemon zest (3 lemons)

Preheat oven to 325°F with the rack in the center. Butter a 10-inch tube pan; set aside. In the bowl of an electric mixer fitted with the paddle attachment, cream butter and sugar on medium speed until light and fluffy, about 3 minutes. Add eggs one at a time, beating well after each addition and scraping down the sides of the bowl. Sift together flour, baking soda and salt into a medium bowl. Add the flour mixture to the butter mixture in 3 additions, alternating with buttermilk and beginning and ending with the flour mixture. Stir in lemon zest and juice. Gently fold in blueberries. Pour batter into prepared pan, smoothing the top with a rubber spatula.

Bake until tester inserted into the center comes out clean and the cake has begun to pull away from the sides of the pan, about 1 hour and 15 minutes. Transfer the pan to a wire rack to cool for 10 minutes.

Meanwhile, prepare the glaze. In a small bowl, whisk together confectioners sugar, lemon juice and lemon zest until smooth; set aside.

Invert cake onto a rack. Prick the surface numerous times with a toothpick. Brush the glaze over the surface of the warm cake and cool to room temperature. Store wrapped in plastic for up to 2 days at room temperature.