Pissaladière~ A French Tart with Caramelized Onions, Mushrooms & Tomatoes

INGREDIENTS

• 2 tablespoons unsalted butter
• salt & freshly ground pepper to taste
• 2 vidalia onions, thinly sliced
• 2 sprigs thyme
• 1 teaspoon thyme leaves
• 15 grape tomatoes, halved lengthwise
• 10 small niçoise olives, halved lengthwise
• 1 sheet frozen puff pastry, thawed
• 1 large egg yolk, ligtly beaten with one tsp water
• 1 packet sliced medley of mushrooms, shitake & baby portobello
• 1 tablespoon extra virgin olive oil
• 2 cloves of garlic, chopped
• 1 sprig rosemary