1.Steam or boil whole unpeeled potatoes until tender; drain. Cool potatoes slightly; peel. Mash potatoes with a ricer, mouli or masher until smooth; stir in garlic and milk. Stir in egg yolks, grated parmesan and enough of the flour to form a firm dough.
2.Roll a quarter of the dough on lightly floured surface into a 2cm-thick sausage. Cut into 2cm lengths; roll into gnocchi-shaped ovals. Place each oval in palm of hand; press with inverted floured fork tines to flatten gnocchi slightly and make a grooved imprint. Place on lightly floured tray in single layer. Cover; refrigerate 1 hour. [Can be made a day ahead to this stage and refrigerated, covered, or frozen for up to 3 months.]
3.Cook gnocchi, in batches, in large saucepan of boiling water about 3 minutes or until gnocchi float to the surface. Remove from pan with slotted spoon; drain.
4.Meanwhile, cook butter in small shallow frying pan until just browned. Add sage; immediately remove from heat. Divide gnocchi among serving plates; drizzle with sage butter. Serve topped with parmesan flakes, and pepper.