In a large mixing bowl, combine the flour, poppy seeds, sugar, baking powder, and salt. Stir well to combine all the dry ingredients.
In another bowl, whisk together the egg, buttermilk, melted butter, lemon zest, lemon juice, and vanilla extract until fully blended.
Pour the wet ingredients into the dry ingredients. Gently fold the mixture with a spatula until just combined. Avoid overmixing; a few lumps are okay!
Preheat a non-stick skillet or griddle over medium heat. Lightly grease with cooking spray or butter.
Pour 1/4 cup of pancake batter onto the skillet for each pancake. Cook for about 2-3 minutes, until bubbles form on the surface and the edges begin to look set.
Flip the pancakes and cook for another 2-3 minutes, until golden brown. Adjust the heat as necessary to prevent burning.
Repeat with remaining batter, greasing the skillet as needed.
Serve the pancakes warm, dusted with powdered sugar, and topped with fresh fruit, if desired.