Can I substitute agar-agar powder for gelatin in no-churn ice cream?
Sure, why not.
350ml of liquid with 0.5g of agar-agar powder.
Just use another 50ml of milk for this 0.5g of agar-agar powder. Before boiling it, mix 0.5g agar-agar powder with around 5 to 15ml of warm water to avoid cobble up and then only boil with the 50ml of milk.