Preheat the oven to 400ºF. Line a 12-cup muffin pan with paper liners.
Using a stand mixer fitted with the paddle attachment or with an electric handheld mixer, beat the butter and sugar on medium speed until light and fluffy.
Turn the speed down to low and beat in the eggs, one at a time. Beat in the yogurt, lemon juice, lemon zest, and vanilla. Make sure the zest isn't clumped in the batter before adding the dry ingredients.
In a separate bowl, whisk the flour, poppy seeds baking powder, baking soda, and salt together. Add it to the butter mixture and use a silicone spatula to mix until just combined.
Divide the batter evenly between the muffin cups. Bake for 12-15 minutes or until a toothpick inserted into the center comes out with only a few moist crumbs attached.
Remove the muffins immediately from the pan and place them on a wire rack to cool completely. Take care when doing this. The pan and muffins will be very hot.
Notes
Yogurt: Be sure to use Greek yogurt, not regular yogurt. Greek yogurt is much thicker and is required to achieve the proper texture for these muffins.
Lemon: Use fresh lemon juice for the best results and use both the zest and the juice.
Zesting lemon: When zesting the lemon, avoid going down to the pith. This will cause the muffins to taste bitter. A microplane works best for zesting citrus.
Thick batter: The batter is meant to be thick and scoopable.
Mini muffins: Bake these in a mini muffin pan. The baking time will be less, about 9-11 minutes. Keep an eye on them while they bake.
Make ahead tip
Muffins are best the day they are made but they can be stored for later use. Place the muffins in an airtight container and keep them at room temperature for up to 3 days.
Muffins will keep for up to 1 week in an airtight container stored in the refrigerator.
They can also be frozen for up to 3 months. Thaw one or all of the muffins in the refrigerator overnight. Or place a single frozen muffin in the microwave for 40-60 seconds.