For the stuffed whole wheat pasta pockets with sage butter, knead the pasta dough ingredients into a firm, smooth dough (5 minutes with the dough hooks, 5 minutes by hand). Wrap the dough in plastic wrap and let it rest at room temperature for at least ½ hour.
For the filling, defrost the spinach leaves in a sieve, squeeze well and chop smaller. Chop the tomatoes, chop the garlic. Mash the feta with a fork, mix with the remaining ingredients and season with salt.
Roll out the pasta dough on the oiled work surface to a thickness of about 2 mm. Either cut out circles with a diameter of 8 cm, or cut squares. Place 1 heaping teaspoon of the filling in the center of each pasta square, fold it up and press the edges well (possibly with the tines of a fork).
Simmer dumplings in salted water for 3-5 minutes. Meanwhile, melt the butter in a frying pan and briefly fry the chopped or crumbled sage leaves in it.
Serve the filled wholemeal dumplings with the sage butter.