Place milk, cream and butter in a pan and gently warm.
Peel the onion and then push cloves into the flesh.
Add studded onion, peppercorns, bay leaves, sugar and garlic to milk-cream liquid; simmer 1 hour on low.
Pour yourself a nice glass of sherry; sip, pet dogs, etc.
Cut loaf into ½-inch squares, toss in a little oil with a sprinkling of kosher salt and toast in the oven until sexy and golden (can be made a day ahead and kept airtight).
Strain the milk-cream mixture and put liquid in a clean pan. Add the mace and then salt to taste.
When you are ready to serve, place the croutons in a warm bowl. Warm the sauce and drizzle it around croutons, sprinkle with fresh thyme and a few twists of fresh cracked black pepper.
NOTE: Bread Sauce is a wonderful way to use up stale bread. The creamy sauce is terrific with roasted poultry—try it with goose, turkey, guinea fowl or, of course, good old chicken.