How To Make Easy French Dip Sliders

Name: How To Make Easy French Dip Sliders
Yield: 6
Ingredients: 1 Tbsp olive oil; 2 Tbsp butter; 1 large or 2 medium yellow onions, thinly sliced; 1/4 tsp sugar; 1 oz packet au jus mix, made according to package instructions; 3 cups water, to make the sauce, or to taste; 16 Hawaiian sweet rolls; 1/4 cup mayo 1 lbs deli pastrami or roast beef, thinly sliced; 9 slices mild provolone cheese (not aged); 2 Tbsp unsalted butter, melted, plus more to grease baking sheet; 1 Tbsp sesame seeds