Preheat your oven to 375°F (190°C). Line a muffin tin with paper liners or lightly grease it to prevent sticking.
In a medium bowl, whisk together 2 cups of all-purpose flour, 1 tbsp of baking powder, 1/2 tsp of baking soda, and 1/4 tsp of salt. Set aside.
In a large mixing bowl, cream 1/2 cup of unsalted butter and 1 cup of granulated sugar until light and fluffy, about 3 minutes using an electric mixer.
Add 2 large eggs one at a time, beating well after each addition. Mix in 1 tsp of vanilla extract, zest of 2 lemons, and 2 tbsp of lemon juice until well combined.
Alternately add the dry ingredients and 1 cup of buttermilk to the wet mixture, starting and ending with the dry ingredients. Mix until just combined, being careful not to overmix.
Fold in 2 tbsp of poppy seeds until evenly distributed throughout the batter.
Divide the batter evenly among the muffin cups, filling each about 3/4 full.
Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Allow the muffins to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.