Preheat the oven to 400°. Prepare the donut pan by coating with nonstick spray.
Combine the flour, cornstarch, sugar, baking powder, baking soda, poppy seeds, salt and lemon zest in a large mixing bowl. Whisk thoroughly.
In a small bowl, combine the non-dairy milk, oil, lemon juice and vanilla extract. The mixture will slightly curdle.
Add the wet ingredients to the dry ingredients and stir to combine.
Pour the batter into a pastry bag or a large Ziploc bag. If using a Ziploc bag, cut the corner. Pipe the batter into the pan.
Bake in the preheated oven for 10-12 minutes depending on the size of the donut pan.
When done, remove from oven and let sit for 5 minutes before removing from the pan and cooling on a wire rack.
Meanwhile, make the glaze. Stir together the confectioners sugar, non-dairy milk, lemon juice, lemon extract and vanilla extract.
Dip the donuts into the glaze and return to the cooling rack.
Store donuts in an airtight container for up to 3 days.
Notes
There are different sizes of donut pans. Mine make pretty small donuts which I actually love. If you're also using a smaller donut pan you might get more than 12 donuts out of the recipe.
I love a strong lemony flavor so I use the zest from a whole lemon. If you want it to be more subtle, use can use it from half a lemon.