Preheat the oven to 350F/177C. Prepare your muffin tins by lining the cups with liners, or use a starched baking spray and spray the inside of the tins very well. This recipe will make 12 jumbo muffins or 24 regular, cupcake size muffins.
In a measuring cup, combine the milk and lemon juice to make buttermilk. Whisk the lemon juice into the milk and let it stand for 5 minutes. You can also use store-bought buttermilk. Meanwhile, in a large mixing bowl, combine the eggs, sugar, oil and vanilla. Beat for 2 to 3 minutes, until the eggs are smooth. Add in the soured milk and mix again for a minute, until well combined.
In a separate bowl, combine the dry ingredients: flour, baking soda, baking powder and salt. Sift the dry ingredients into the muffin batter, then mix just until incorporated, about 1 minute. Do not overmix the batter! Add in the poppy seeds and zest from 2 to 4 lemons, then stir to combine. Watch my video recipe to see how I make these!
Fill each muffin tin with batter, filling the tin a little more than 1/2 way. Do not overfill the tins; the batter rises quite a bit! Bake the muffins in the preheated oven for 27 to 30 minutes if using jumbo muffin tins, until the tops are golden brown. If using regular, cupcake tins, reduce the baking time to 22 to 25 minutes.
Next, prepare the glaze. In a medium bowl, combine the confectioner's sugar and lemon juice. Whisk to combine and then add more milk as needed for a thinner glaze. The glaze should flow easily over the muffins. Use a pastry brush to brush the glaze over warm muffins.
How to freeze: If you are not planning to enjoy them all right away, consider freezing them for later! Just allow the muffins to cool completely, then place into an airtight container and into the freezer. When you're ready to enjoy them again, take them out and thaw at room temperature for 30 minutes to an hour, until they're soft again.