Pour the milk into a non-reactive saucepan. Add the onion, bay leaf, parsley, oregano and peppercorns. Heat until scalded. Remove from heat and allow to sit for 30 minutes.
Strain milk, return to pan and reheat to scalding.
In a heavy medium-sized saucepan, melt the butter or margarine.
Stir in the flour. Cook over medium heat, stirring constantly, for 2 to 3 minutes without browning.
Pour in the hot milk. Whisk until mixture bubbles and thickens.
Remove from heat and stir in 3 cups of the cheese, stirring until melted.
Season the cheese sauce with salt and Tabasco.
Fold in the cooked macaroni.
Pour into a greased 1 1/2 quart casserole. Top with remaining cup of cheese.
Bake in the center of a preheated 350º oven for 25 to 30 minutes or until bubbly.