Place bayleaf, parsley stalks, onion slice, peppercorns and thyme in saucepan, add milk.
Bring slowly to boiling point, remove from heat, stand 5 minutes.
Melt butter in saucepan, remove from heat, add flour, stir until smooth, gradually add strained milk, stirring constantly.
Return to heat, stir until sauce boils and thickens.
Season to taste with salt and pepper.
Pour over pancakes