Preheat the oven to 325°F (163ºC). Spray a 12-cup bundt panwith nonstick baking spray and add a few tablespoons of all-purpose flour to the pan, shake it around to coat well, remove any tap out, and throw away any excess.
In the bowl of an electric stand-up mixer, gradually beat butter (1 1/2 cups) until it's creamy. Add sugar (3 cups) and beat at medium speed for 5-7 minutes, or until the mixture is light and fluffy. (I beat for 7 minutes). Add eggs (6), one at a time, beating just until the yolk disappears and is incorporated into the batter
In a medium bowl, mix together flour (3 cups), salt (1/2 teaspoon), and baking soda (1/4 teaspoon). Add to butter mixture, alternating with sour cream (1 cup), beginning and ending with the flour mixture. Beat batter on low just until blended after each addition. Stir in vanilla (2 teaspoons).
Using a rubber spatula, fold in blueberries (2 cups). Continue to fold until they're mixed evenly throughout the batter.
Pour the batter into the prepared pan, filling the pan only 3/4 full, and bake in the preheated oven for 1 hour and 20 minutes to 1 hour and 40 minutes, testing until a wooden skewer or cake tester, is inserted into the center of the cake just comes out clean, without any crumbs. Cool pan on a wire rack for 10-15 minutes, then invert the pan onto a plate, remove the cake from the pan, and cool completely
Glaze:
Meanwhile, make the glaze: add powdered sugar (1 1/2 cups) to a medium bowl. Add milk or cream to powdered sugar, 1 tablespoon at a time as needed, mixing well after each addition, until you reach the desired, pourable consistency. Pour over completely cooled cake. Let the cake sit for the glaze to set, then serve.
Notes
Bundt Pan: The size of the bundt pan really matters. I use a 12-cup bundt pan and the cake batter comes up to about an inch from the top. The batter has never overflowed from this size pan. Do Not use a smaller size pan.
Baking Time: It’s REALLY important to make sure the cake is baked completely, but not overbaked. Under-baked pound cake won’t come out of the pan smoothly; over-baked will be dry. To test for doneness skip the toothpick and use a bamboo skewer. I prefer my pound cakes to have just a few moist crumbs clinging to it. If there is batter clinging to the skewer it is underdone and not baked properly
Stand Mixer: I like to use my stand mixer fitted with the paddle attachment because of the long beating time need to create the wonderful texture of this cake.
Thick Batter: Be sure to scrape down the sides of the bowl throughout mixing.
Slicing Cake: Use a serrated knife to neatly slice the cake.