Prep the onions by peeling, halving, and slicing them rather thickly.
Melt the butter in a large, heavy-bottomed pot over medium heat.
Add the bay leaves and minced garlic, stirring constantly for about 1 minute until fragrant.
Add the sliced onions and increase the heat to medium-high.
Sauté, stirring almost constantly, for at least 30 minutes. Be patient; you want the onions to become an even, caramelized light brown color.
Stir in the paprika and salt and continue to cook for another 2-3 minutes to toast the spices.
Pour in the red wine, scraping up any browned bits from the bottom of the pot.
Add the thyme, cayenne, basil, oregano, sage, tomatoes, brandy, lemon juice, vinegar, and a generous amount of black pepper.
Reduce the heat to low and let the sauce simmer, stirring occasionally, for 45 to 60 minutes. It should become thick but remain saucy, not pasty.
While the sauce simmers, bring 6-7 quarts of generously salted water to a boil.
Cook the spaghetti until it is just al dente, then drain it immediately.
Taste the sauce and adjust seasoning if necessary. Remember to remove the bay leaves.
Pour the hot sauce over the drained spaghetti, toss together quickly to coat, and serve immediately.
Don't rush the onion caramelization. The 30+ minutes of slow cooking is what develops the deep, sweet, and savory foundation of the sauce.
Before draining the spaghetti, reserve about a cup of the starchy cooking water. If your sauce is a bit too thick, add a splash to the final dish to help it emulsify and cling perfectly to the pasta.