Preheat oven to 350 F. Line muffin pan with cupcake liners.

Grate the zest first and then squeeze the juice of one lemon into a measuring cup. Add the almond milk until you reach 1 cup of liquid. Set aside for a few minutes to get curdled.

Sift the flour, cornstarch, baking powder, baking soda, and salt into a large bowl and mix.

Mix in a large bowl sugar and lemon zest with your fingers, releasing all the oils from the zest.

Mix together the almond milk mixture, oil, sugar, vanilla extract and whisk until well combined.

Sift in the flour, cornstarch, baking powder, baking soda, and salt, and mix until no large lumps remain.

Fill cupcake liners two-thirds of the way and bake for 20 to 22 minutes.

Transfer to a cooling rack to cool.

For the Lemon Buttercream

In a large mixing bowl, beat the vegan margarine with an electric hand mixer until smooth.

Add the lemon juice, lemon zest and vanilla extract and mix to incorporate. Add the icing sugar 1 cup at a time, and beat on medium speed until the frosting is very thick and very smooth.