Melt butter and olive oil in skillet over medium heat.

Add sliced onions to pan, season with salt and pepper and cook, continuing to stir, until tender and golden brown (this process takes a while- up to 20 minutes) then set aside.

Preheat oven to 425 degrees.

Using a round cookie cutter, cut circles of dough out of puff pastry and place on a parchment paper lined baking sheet.

Brush egg wash on each pastry circle then top each with a tomato slice in the direct center.

Next add caramelized onions on top of each tomato slice and sprinkle shredded cheese.

Bake for 16-20 minutes or until tarts are puffy and golden brown and cheese has turned golden and melty. Top with parsley and herbs if you would like. Cool for a few minutes then serve.