1) Preheat the oven to 375°F. Line a muffin tin with papers, and grease the papers.
2) In a medium-sized bowl, whisk together the flour, baking powder, baking soda, and salt, then set aside.
3) In a large bowl, beat the butter and sugar with a hand-held or stand mixer, until light, fluffy, and almost white in color. Start the mixer at low speed until the ingredients are incorporated, then gradually increase speed to medium-high until the desired color and texture are reached.
4) Scrape down the bowl to make sure all the butter is incorporated, then add the eggs one at a time, beating well after each addition.
5) Add the vanilla and sour cream or yogurt, and mix until incorporated.
6) Add the dry ingredients and mix on low speed just until the batter is smooth. It will be thick.
7) Fold in the berries by hand.
8) Scoop the batter into the prepared muffin cups, using a heaping 1/4-cup for each. Sprinkle with regular granulated or coarse white sugar, if desired.
9) Bake the muffins for 18 to 24 minutes, until a cake tester inserted in the center of one comes out clean. Remove them from the oven, cool in the pan for 5 minutes, then remove the muffins from the pan to finish cooling on a rack.
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