From the Cook's Illustrated Website: This recipe does not require a standing mixer, but when making the batter, be sure to whisk vigorously in step 2, then fold carefully in step 3. There should be no large pockets of flour in the finished batter, but small occasional sprays may remain. Do not overmix the batter. These muffins are great unadorned, but for an extra flourish, give them a dip in sugar by following one of the variations. Makes 12 muffins
- Adjust oven rack to middle position and heat oven to 350 degrees. Spray standard muffin tin with nonstick vegetable cooking spray.
- Whisk flour, baking powder, and salt in medium bowl until combined. Whisk egg in second medium bowl until well-combined and light-colored, about 20 seconds. Add sugar and whisk vigorously until thick and homogenous, about 30 seconds; add melted butter in 2 or 3 steps, whisking to combine after each addition. Add sour cream in 2 steps, whisking just to combine.
- Add frozen berries to dry ingredients and gently toss to combine. Add sour cream mixture and fold with rubber spatula until batter comes together and berries are evenly distributed, 25 to 30 seconds (small spots of flour may remain and batter will be thick). Do not overmix.
- Use ice cream scoop or large spoon to drop batter into greased muffin tin. Bake until light golden brown and toothpick or skewer inserted into center of muffin comes out clean, 25 to 30 minutes, rotating pan from front to back halfway through baking time. Invert muffins onto wire rack, stand muffins upright, and cool 5 minutes.