Chop the onion.
Boil the spaghetti according to package instructions. Drain the water. Put the onion, bay leaf in a saucepan with milk, bring to a boil. Remove from heat and let stand 20 minutes. Thoroughly mix the flour in the heated oil. Pour warm milk into the flour mixture and stir the sauce until smooth. Bring the sauce to a boil. Mix crushed peppercorns, grated nutmeg and add to the sauce. Pour the grated cheese into the sauce, heat without boiling, cook, stirring, 5 minutes.
Spaghetti served with cheese sauce!