Begin by weighing and pouring the liquid from two cans of chickpeas into a saucepan over medium heat. Simmer the aquafaba until it's reduced by half, around 10-15 minutes, stirring occasionally. Allow it to cool and then refrigerate overnight.

Preheat your oven to 150°C (300°F) or 130°C (275°F) for fan ovens. Prepare two non-stick baking sheets lined with parchment paper.

In a large mixing bowl, extract your chilled aquafaba and add a pinch of cream of tartar. Whip with an electric mixer until frothy, gradually adding caster sugar until you achieve stiff peaks.

In a separate bowl, sift together ground almonds and icing sugar. Carefully fold the dry mixture into the whipped aquafaba in two batches, working gently to maintain airiness.

Fill a piping bag and pipe 2-inch circles onto the baking sheets, leaving space between each macaron. Let sit at room temperature for 20-30 minutes until a skin forms.

Bake the macarons for about 18 minutes. Check doneness by gently wiggling the shells; they should not wobble.

Once cooled, carefully peel the macaron shells off the parchment paper and pair similar-sized shells.

In a mixing bowl, combine icing sugar and vegan margarine, mixing until creamy. Add vanilla for flavor and stir in plant-based milk if too thick.

To assemble, pipe buttercream onto one macaron shell and press another shell on top. Store in an airtight container in the fridge.