Preheat the oven to 180°C and line 2 baking trays with baking paper.
Beat the dairy-free margarine and sugar together until combined and looks pale and like buttercream. Approximately 2 minutes.
Add the egg and vanilla. Beat until combined; it will be a runny consistency and the mix will look slightly separated.
Mix in the gluten-free flour, baking powder, and salt until combined. It should be pulling away from the bowl when you stir the dough.
Add the rice milk and stir.
Add in flavours here. See notes.
Scoop it out onto the trays using 2 spoons or ice cream or cookie scoop.
Bake for 12-14 minutes, rotating the trays ½ way through the cooking time.
Store in an airtight container for 2-3 days.