Preheat oven to 350°F. Line a 12 cup muffin tin with muffin liners.
In a mixing bowl, sift the flour, baking powder, and salt together. Then, mix in poppy seeds. Using a mixer, beat the butter and sugar on medium-high for 3 minutes.
Add in zest of 2 lemons and lemon juice. Mix until combined. Scrape the bowl. Add in the eggs one at time on low. Scrape the bowl.
Add in ⅓ of the dry ingredients and half of the buttermilk .Mix until just combined. Add in another ⅓ of the dry ingredients and the rest of the buttermilk. Mix. Add the rest of the dry ingredients. Scrape the bowl and mix for 10-15 seconds.
Use 1 ½ tablespoon cookie scoop to scoop the batter into the muffin tins. Fill them ⅔ full.
Bake for 16-18 minutes. The cupcakes are done baking when a toothpick inserted comes out clean. Let the cupcakes sit in the tin for 10 minutes before transferring to a cooling rack. Then allow them to cool completely.
Lemon Cream Cheese Frosting
Let the butter sit for 30 minutes on the counter to get slightly cold. While waiting, sift the powdered sugar. Beat the cream cheese on high for 1 minute before adding the butter. Beat for 1-2 minutes until smooth. Scrape the bowl.
Slowly add in the powdered sugar. Scrape the bowl. Add in zest of 1 lemon, lemon juice, and heavy cream. Mix on low until just combined. Mix on high for 1 minute until light. Then, decorate. Keep in the fridge.
Flour- Spoon and level flour or use a kitchen scale. Compacted flour can dry out the cupcakes.High altitude baking- Add an extra 1 tablespoon of flour.