Heat 1 tablespoon of the oil in a large heavy pan, when hot, brown the roast on both sides while seasoning with salt and pepper. Remove the roast to a plate and set aside.

Same pan add the remaining oil and add the onions and cook until they just start to soften and wilt then add the garlic and cook a few more minutes until the onions are translucent.

In a measuring cup, add the hot water and the bullion cubes and mix to dissolve, then pour that into the pan, also to the pan, add the beer, brown sugar, vinegar, and stir to mix well.

Pour the mixture, carefully, into your slow cooker insert, place the roast on top of that mixture. Switch the slow cooker to Low setting for 7-8 hours. Check for tenderness at 7 hours. If needed, continue to cook until the roast is tender to your liking.

When the roast is tender, remove from the slow cooker and place on a platter. Pour the liquid from the slow cooker into a saucepan on the stove and bring to a boil.

While the liquid is heating, mix together a slurry of 1-2 tablespoons of cornstarch and 2-3 tablespoons of cold water, stir into the liquid until the gravy is thickened to your liking.

Serve with mashed potatoes or pasta, spoon gravy over slices of roast and potatoes.