Thaw frozen spinach by placing it in the refrigerator overnight. Be sure to put the bag or block of frozen spinach in a bowl or on top of a plate, to collect the water that leaks while thawing. You can also thaw frozen spinach in your microwave, using your "defrost" button and entering the weight of the spinach you're thawing. Place the spinach on a plate or in a bowl inside the microwave while it is thawing. Flip the spinach halfway through to help it defrost evenly.