Make dough: mix flour and eggs into a ball; knead briefly until smooth; wrap and rest 30 minutes.
Roll small portions through pasta machine repeatedly to thin sheets.
Blanch spinach 3 minutes; drain and squeeze dry; chop. Process spinach with egg yolk and ricotta; season.
Cut pasta sheets into rounds (or squares). Place 1 tsp filling on half the pieces; lightly moisten edges; top with second piece and seal well, expelling air.
Boil ravioli 3–5 minutes in salted water until al dente. Drain; serve drizzled with olive oil or sauce of choice.