Preheat the oven to 400℉. Lightly spray a mini muffin pan and set aside.
In a large bowl, cream together the butter and sugar. Mix in the lemon zest. Add in the egg and mix until smooth.
In a separate bowl, mix together the flour, baking powder, salt and poppy seeds.
Slowly mix the dry ingredients into the sugar mixture. Add in the lemon juice and buttermilk, and mix until just combined.
Spoon the batter into the prepared muffin cups and bake in the preheated oven for 10 minutes.