Spoon the ricotta cheese into a sieve placed over a bowl and refrigerate for 2 hours to drain off the liquid. If using fresh spinach, cook it in the rinsing water clinging to the leaves until wilted, 3 to 5 minutes. Drain well and chop finely. If using thawed, frozen spinach, squeeze dry.
Melt the butter in a large sauté pan over medium heat and let it color just slightly. Add the spina