Place the flour in a bowl, create a well in the middle and add the egg with a pinch of salt.
Mix it all together, adding the water little by little, until a thick dough forms. Knead the dough for a few minutes and then put to the side.
Heat a saucepan with the olive oil and then cook the spinach. Remove from the heat and mix in the ricotta cheese.
Place the dough on a floured surface and knead for a few more minutes.
Roll the dough out using a rolling pin, or pasta machine, and then cut in to small squares with a pasta or pizza cutter.
Place the egg yolk in a dish and beat with a pinch of salt. Take a pastry brush and brush yolk on to the dough squares. Place a spoonful of ricotta filling on a dough square.
Place another dough square on top and score around the edges with a fork.
Make as many as you want and then cook in a pan of boiling water for a minute before draining and serving. I suggest serving with <a href="/blog/project.php?id=161">pesto</a> and a sprinkling of ricotta.