Preheat your oven to 400 F and prepare your muffin tins. You can either use paper liners, silicone liners, or grease them with cooking spray or coconut oil rubbed inside each tin.
In a large bowl or stand mixer, combine the flour, baking powder, baking soda, poppy seeds, sugar and salt.
In a medium bowl, whisk together the milk, maple syrup, if using in place of sugar, melted butter, eggs, lemon juice and vanilla until well combined.
Slowly add the wet ingredients to the dry ingredients and gently combine. Be careful not to over mix. If using a stand mixer, run on low until well combined.
Spoon the batter into the prepared muffin tin.
Bake for 20 minutes, or until a toothpick inserted in the middle comes out clean. The edges of the muffins should start to turn golden brown when done.
Remove to a wire rack to cool.
For the glaze, whisk the powdered sugar and lemon juice in a small bowl until combined. Then, you can either drizzle it over the top, or add it to a piping bag. I use a ziplock bag with the corner clipped off.