Roast Beef 'n Swiss Sandwich with Onions & Horseradish

Our butcher cut the most beautiful 5 pound rump roast that I seasoned it generously with freshly ground black pepper, kosher salt, garlic powder, and lemon pepper.  It was dry roasted it fat side up in a covered cast iron dutch oven for just under 3 hours, to perfection, at 325 degrees F.  Upon removing it from the oven I left it covered until cool enough to handle, an hour or so.....

Using a large chefs knife I sliced it as thinly as possible and transferred it to a large shallow covered glass casserole to reheat at serving time.  Meanwhile slice a couple of large sweet onions and saute them in a couple of tablespoons of butter or olive oil until a succulent golden brown and the aroma in the kitchen is wonderful!!

Butter the French rolls and toast them under the broiler.  Strain the Au Jus from the original roasting pan and transfer it to a small dish or gravy boat.  Assemble the sandwiches with sliced beef, Swiss cheese, onions,  and horseradish sauce along side the Au Jus for dipping.  Be ready for smiles at the table, this one always works for me!!