Savory Thyme Tart

Name: Savory Thyme Tart
Ingredients: 1 1/2 cups ricotta cheese; 1/3 cup freshly grated Parmesan; 3 tablespoons lemon juice; kosher salt and black pepper; 2 tablespoons fresh thyme leaves; flour for work surface; 1 sheet puff pastry; 1 small onion, very thinly sliced; 2 tablespoons olive oil; 2 tablespoons pine nuts