Let frozen spinach thaw before adding them to your filling. It is important to squeeze any excess water out of it. Otherwise, it will thin your filling significantly. Usually, a bag of frozen spinach of 10 oz (0.38 kg) equals to 1 pound (0.45 kg) of fresh leaves. In this recipe, we used 4 oz (0.15 kg) fresh spinach leaves so that you can substitute it with 2 oz (75.6 g) frozen spinach.