Preheat the oven to 425°F.
In a medium sauce pan set over medium heat, add the butter and onions and cook, stirring, until the butter is melted.
Add the sugar and cook, stirring occasionally, until the onions are caramelized, about 20 minutes. Add the garlic, thyme and rosemary and cook until garlic is golden, about 5 minutes. Transfer the mixture to a bowl to cool completely.
In a stand mixer fitted with paddle attachment, beat together the goat cheese, cream cheese , eggs, ½ teaspoon salt and ¼ teaspoon pepper. Add caramelized onion mixture and mix.
Lightly flour your work surface then unfold the puff pastry and use a rolling pin to lightly roll over and seal any creases.
Prick the center of the pastry all over with a fork then score a 1-inch border around all of the edges.
Spread the cream cheese mixture on top of the pastry, keeping it within the docked border. Top the cream cheese mixture with the sliced tomatoes.
Bake the tart until it is golden brown and puffed, about 25 minutes. Remove it from the oven and let it cool for 10 minutes before slicing and serving with a drizzle of balsamic syrup (optional).
★ Did you make this recipe? Don't forget to give it a star rating below!