Preheat the oven to 350F degrees and line 2 muffin pans with liners. You'll end up with about 14 cupcakes in total.
In a large bowl sift together the flour, baking powder, baking soda and salt. Give them a whisk.
In a separate large bowl, beat the butter, sugar and lemon zest until fluffy.
Beat in the eggs and vanilla extract.
With the mixer on low speed, beat in about 1/2 of the sour cream followed by about 1/2 of the flour mixture. Turn off the mixer and scrape down the sides of the bowl.
Repeat the process with the rest of the sour cream and flour mixture.
Gently fold in the lemon juice and poppy seeds.
Spoon the batter into the prepared muffin pans filling each about 2/3 full. You should get about 14 cupcakes.
Bake 1 tray at a time on the middle rack of the oven for 16-20 minutes, or until the tops look set and an inserted toothpick comes out clean. Cool in the pan for at least 10 minutes, then continue cooling on a wire rack.