3 roasted onion caper and tarragon sauce Recipes

vegetable oil, a 3-lb fillet of beef , halved crosswise, loaves of italian bread (each about 14 inches long), cut diagonally into 1/2-inch slices, olive oil for brushing the bread, garlic cloves, roasted onion , caper, and tarragon sauce, tarragon sprigs for garnish

onions (about 3/4 lb each), unpeeled and untrimmed, unsalted butter, all-purpose flour, heavy cream, dry white wine, drained bottled capers, white-wine vinegar, minced fresh tarragon leaves or 3/4 tsp dried,crumbled, minced fresh parsley leaves, sliced fresh chives or scallion greens