Mix flour, salt and egg yolk. Gradually add water. Then add butter, and keep forming until it's all unified.

Wrap the dough in foil and leave for about 30 minutes.

Fry the spinach in a small saucepan adding pepper and salt. Cool it down for a few minutes. Add crumbled feta cheese and mix it.

Roll the dough (3mm thick). Cut out squares, and put a bit of spinach in the middle. Fold into triangles, press to join the edges. Bring the points of the long side together. Seal between your fingers to form a ring.

Put your tortellini into boiling water, and take them out with a skimmer once their ready.