Rustic Tomato Tart

Name: Rustic Tomato Tart
Prep time: 1 h 25 min
Total time: 1 h 25 min
Cuisine: European, Italian, Mediterranean
Ingredients: 30 grams unsalted butter (2 tablespoons); 250-300 grams onions, peeled and sliced into thin rings (2 medium onions, or 1 large onion); 10 milliliters olive oil (1 tablespoon); 40 grams tomato paste (2 tablespoons); 15 grams ketchup, or sriracha (1 tablespoon); 150 grams ripe red tomatoes, chopped (2 medium tomatoes, or 1 large tomato); 15 grams light brown sugar (1 tablespoon, packed); 1 teaspoon garlic powder; 1 teaspoon paprika; 1/4 teaspoon red pepper flakes (optional); Generous pinch fine sea salt; 15 milliliters lemon juice (1 tablespoon); 200 grams ripe tomatoes, thinly sliced (2 large, or 3 medium tomatoes); 1 sheet puff pastry, thawed according to package directions if frozen; 60 grams blue cheese, crumbled (2 1/4 ounces); 125 grams cherry tomatoes, halved if large (12-14 tomatoes); 15 grams Parmesan or Parmigiano Reggiano cheese, grated (2 tablespoons), plus more to garnish; Salt and pepper, to taste; 1 egg, lightly beaten; 2-3 tablespoons chopped fresh herbs (I used a mix of basil, rosemary and parsley)