Season the brisket generously with salt and pepper on both sides.

Heat the oil in a Dutch oven over medium-high and sear the brisket 4 to 5 minutes per side until deeply browned; remove and set aside.

Add the onions to the same pot and cook over medium heat, stirring occasionally, 20 minutes until soft and golden.

Stir in the garlic and cook 1 minute, until fragrant.

Add the broth, wine, tomato paste, brown sugar and smoked paprika, scraping up the browned bits from the bottom of the pot.

Return the brisket to the pot, cover, and braise in a 325°F oven for 3 to 3.5 hours, until a fork slides in with almost no resistance.

Lift the brisket out, rest 15 minutes, then slice thinly against the grain.

Return the sliced meat to the pot juices to soak for at least 10 minutes before serving.

Pile warm brisket and onions onto slider buns with a smear of horseradish mayo, and serve while the meat is still steaming.