Preheat the oven to 350 degrees F and lightly grease a 9x9 (or 8x8) inch baking pan. Or line it with parchment paper for easy removal.
In the bowl of a stand mixer with the paddle attachment, or using a handheld mixer, beat the softened vegan butter and sugar until creamy.
Add the vanilla, lemon extract, lemon zest, juice and optional yellow food coloring. Mix until combined, scraping the sides and bottom of the bowl as needed.
Stop the mixer and add the flour, followed by the cornstarch, baking soda and salt. Turn the mixer on low speed and mix until just combined.
Spread in the prepared pan, using an offset spatula. The dough is thick, like cookie dough, so be patient and get it as even as possible with either your hands or the spatula.
Bake for 25 minutes, until just set in the center. Don't over bake, or they will be dry.
Let them cool in the pan for about 15 minutes, then lift out using the parchment paper (if using) and let cool completely on a wire rack.
In a small bowl, mix the powdered sugar and lemon juice until thick but pourable. Add additional powdered sugar if needed. Spread over the cooled brownies.
Let the glaze harden before slicing and serving. Enjoy! You can sprinkle a little extra lemon zest on top, if you want.