Preheat the oven to 350 degrees F. Line two 12-cup muffin tins with paper/parchment liners. Set aside.
With an electric handheld mixer (or in the bowl of a stand mixer fitted with the paddle attachment), cream together the cream cheese, butter, and sugar until light and fluffy, 1-2 minutes.
Add the eggs, vanilla, and buttermilk, and mix again until well-combined, scraping down the sides of the bowl as needed.
In a separate bowl, whisk together the flour, baking powder, baking soda, and salt.
Add the dry ingredients to the muffin batter and mix with a wooden spoon or spatula once or twice. There will be a lot of dry steaks remaining. Add the blueberries. Mix until JUST combined. Don't overmix. It's ok if it's slightly lumpy.
Divide the batter evenly among the muffin cups. Bake for 14-17 minutes until the tops spring back lightly to the touch. Don't overbake (the exact time will depend on the variance of temperature in your oven so if you have to add time, that's ok).
Remove the muffins to a wire rack to cool completely. Store in a covered container at room temp or in the refrigerator for several days. The tops of the muffin will soften as they are stored; they reheat beautifully for 10-15 seconds in the microwave and taste fresh as can be even days later.
Notes
Blueberries: I've only ever made these muffins with freeze-dried blueberries, but my friend, Heather, that sent me the recipe makes them with fresh blueberries. I'm not sure how frozen blueberries would fare, but I'm guessing they'd work fine (don't thaw before using!).Lemon: I haven't tried it, but I think a little touch of fresh lemon zest in this muffin batter would take them completely over the top. Whatever you do, don't even think about drizzling a lemony, powdered sugar glaze over the top. I'm sure it would be awful. Just awful.