To make the pasta, sift the flour onto a work surface, forming a volcano-shaped mound with a well in the centre. Break the eggs into the well and add the salt and spinach. Incorporate the eggs and spinach into the flour with a fork and your hands, gradually drawing the flour into the egg mixture until it forms a coarse paste.
Add a little more flour if the mixture is too soft or sticky, or a little water if the mixture is too dry. Using a knife (or a spatula), scrape up any stray pieces of dough.
Before kneading the dough, clean your hands and the work surface. Lightly flour the work surface, and start to knead the dough with the heel of one hand as you might break the dough. Work the dough for 10-15 minutes until the consistency is smooth and elastic. If the dough sticks to your fingers, rub your hands with some flour. Wrap the dough in cling film or aluminium foil and leave it to rest for at least half an hour.
Roll out the pasta, by machine or using a rolling pin, into two long sheets, roughly 15-20cm/6-8in wide, and 2mm thick. Cut the burrata mozzarella into 12 pieces.
Place one sheet of pasta on the work surface. Put six pieces of mozzarella evenly along one side of the pasta sheet, and sprinkle with half of the parmesan.
Brush around the pieces of cheese with water and fold over the other side of the pasta sheet. Cover the six pieces of cheese by pressing the dough all around each to expel the air. Cut into rectangles with a pasta wheel or a sharp knife to make six large ravioli. Cover with a tea towel while you make the remaining ravioli.
Repeat with the other pasta sheet, using the rest of the burrata pieces and the remaining parmesan.
Cook the ravioli gently in plenty of boiling salted water for 2-3 minutes or until al dente. Melt the butter in a pan with the pine nuts and rosemary. Let the hot butter absorb the herb flavour for two minutes. Scoop the ravioli out of the water and place in the pan with the melted butter and pine nuts.
Serve the pasta on warmed plates, sprinkled with more parmesan.