Mix flour, baking powder, salt, poppy seeds, and lemon zest in a bowl and set aside.

In a separate bowl, whisk together the light brown sugar, sugar, eggs, oil, whole milk, lemon juice, and vanilla.

Right before you are ready to bake the muffins, pour the wet mixture into the dry mixture and fold with a rubber spatula until just mixed (this will activate the baking powder – as the mixture sits and soaks, it will become less active, so waiting to mix until right before the muffins go into the oven is very important). Do not over mix the batter. It should be clumpy, but you want to make sure the majority of the flour is incorporated and there are no large spots of flour.

Place paper liners in muffin tin and fill ⅔-¾ of the way full with batter.

Place the filled muffin pan on a baking sheet – this will help to keep the bottoms from burning.

For the lemon glaze, mix all ingredients together with a spatula until smooth and transfer into pastry bags to decorate the baked and cooled muffins.