When you have 3 potatoes, make these crispy potato rings

ingredients : 3 medium potatoes (500g). salt. 5 cloves of garlic. 2 tablespoons of butter (30g). half an onion. 3/4 cup of water (150ml). 5 tablespoons of all purpose flour (40g) parsley. 1/2 cup of cornstarch (50g). vegetable oil for frying.