Have a piping bag with a suitable tip ready. Assemble your cookies.
For the topping combine agar agar, water, and 200 g sugar in a pot and place on the stove, but don't heat it yet.
In a large bowl, whisk aquafaba until foamy, for about one minute.
Add lemon juice.
Then slowly add 100 g sugar to the mixture.
Beat the mixture for about 10 minutes until very stiff peaks will form.
Add guar gum and beat for another minute.
Add food colouring, if using, and mix until incorporated. (I used 8 g of spirulina powder.)
Once the mixture is very stiff, transfer to a heat-proof bowl.
Now bring the agar mixture to a boil and cook for three minutes. Remove from heat and stir briefly, so the sticky bits from the bottom get dissolved.
Now you need to work quickly: Have the heatprof bowl with the agar mixture and your handheld mixer ready.
Start whisking the aquafaba mixture again and slowly pour in the hot sugar syrup.
Once the sugar syrup is incorporated, transfer the mixture to a piping bag with your favourite tip and pipe on top of the cookies.
Place in the fridge to cool for 30 minutes.
Melt 300 g of chocoolate in a double boiler.
Transfer to a mug and dip the marshmallows into the chocolate.
You can also use a spoon to cover the marshmallows: Place the marshmallows over the mug and drizzle the chocolate all over.
Place on a cookie rack and let the excess chocolate drain from the marshmallows.
Transfer to the fridge and let set completely.