Preheat the oven to 400°F. Line a standard muffin tin with paper liners.
In a large bowl, whisk together the flour, sugar, poppy seeds, baking powder, baking soda, and salt.
In a small bowl, whisk together the milk, butter, egg, juice, and zest. Pour into the dry ingredients and stir with a rubber spatula until just combined. Do not overmix - there should be a couple streaks of flour remaining.* Divide evenly among the muffin tin cups.
Bake until golden brown and a toothpick inserted in the center comes out clean and the edges are golden, about 15 minutes. Let cool until barely warm.
Serve, or store in an airtight at room temperature for 3 days. Muffins can also be frozen in an airtight container for up to 3 months.