Caramelize the Onions: Melt the Butter in a large skillet over medium-low heat. Add the Onions and cook slowly, stirring occasionally, for 30-40 minutes, until deeply golden brown and caramelized. Set aside.
In a separate large skillet, brown the Beef over medium-high heat. Drain off any excess grease.
Add the Garlic to the skillet and cook for 1 minute more.
Deglaze the pan with the Red Wine, scraping up any browned bits from the bottom. Cook until the wine has almost completely evaporated.
Add the Tomato Paste and all remaining Sauce ingredients to the skillet. Bring to a simmer and cook for 30-40 minutes, stirring occasionally, until the sauce has thickened and deepened in flavor.
Stir in the Caramelized Onions.
Lightly toast the Pretzel Slider Rolls. Spoon the Sloppy Joe mixture onto the toasted rolls and serve immediately.
