While that is cooking, cook the spinach. Use fresh spinach and steam it or cook up frozen chopped spinach. There is no set amount to use, but if you use frozen spinach, prepare one package which is 10 ounces. When that is cooked, drain it and squeeze the water out of it. Then, puree it in a food chopper. This step is not necessary if you love spinach. But my kids don't, so I find that if I make it so they don't see big chunks, they are fine with it!