Preheat oven to 350*F. Grease an 8-inch square pan and line it with parchment paper.
In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl using a hand mixer, cream together non-dairy butter, sugar, and lemon zest until light and fluffy.
8 Tbsp Non-Dairy Butter, room temperature, 1 Cup Granulated Sugar, 1 Tbsp Lemon Zest
Add non-dairy milk, lemon juice and vanilla and mix on low until well combined.
3 Tbsp Non-Dairy Milk, 2 Tbsp Lemon Juice, 2 tsp Vanilla Extract
Add the flour, baking powder, baking soda, and salt and mix on low until the dough forms. Then, scrape the dough into the prepared baking pan and use an offset spatula or lightly oiled hands to spread it out evenly.
2 Cups All-Purpose Flour, 1 ¾ tsp Baking Powder, ½ tsp Kosher Salt
Bake in a 350*F oven for 34-37 minutes or until the edges of the bars are golden brown. Allow the lemon cookie bars to cool for 20 minutes before glazing.