Mini Tomato & Mozzarella Tarts

1 package (17.3 ounce) puff pastry dough, defrosted
olive oil
1 large yellow onion, thinly sliced
2 garlic cloves, minced
Kosher salt and black pepper
3 Tablespoons chicken broth
2 teaspoons minced fresh thyme leaves
1/2 cup freshly grated Parmesan cheese
4 ounces fresh Mozzarella cheese, cut into 1 inch cubes
2 Roma Tomatoes, thinly sliced
3 Tablespoons julienned basil leaves