Preheat oven to 400°.
Thinly slice shallots and add to a skillet with 2 tbsp butter, a pinch of salt and pepper. Cook stirring often on medium to low heat for about 15 min or until the shallots are cooked down and a deep brown.
Add all filling ingredients to a bowl and mix to combine.
Unwrap puff pastry and add filling to the middle. Optional: You can cut the edges of this to make it more of a galette shape, or keep it square.
Slice and season tomatoes with olive oil, salt and pepper. After a few minutes the tomatoes will remove some excess liquid, make sure to pat down before adding to the tart.
Add tomatoes to the center of the tart, leaving a border around the parameter. Cut the larger tomatoes into smaller pieces if needed.
Press the edges in and overlap them slightly to create a crust. Brush with egg wash.
Bake for about 30 min or until nicely golden brown. If you like, drizzle the top with balsamic glaze, basil and flaky sea salt.