Preheat oven to 375 F. Line a large baking sheet with parchment paper.
Place tomatoes, onions, garlic and thyme on baking sheet. Toss with olive oil and salt. Roast in the preheated oven for 1 1/2 hours.
Pour the white wine over the tomatoes and roast for an additional 30 mins, until the liquid is almost evaporated and they have caramelized around the edges.
Discard the thyme and transfer the roasted tomatoes, onions, garlic together with all the juices to a medium soup pot. Pour in the vegetable stock and bring to a gentle simmer.
Remove from heat and using an immersion blender puree the soup to your liking.
Adjust seasonings to taste with more sea salt and red pepper flakes. You can also add additional vegetable stock to bring the soup to your preferred consistency.
To serve, pour lemon juice on a small round plate. Mix sea salts and place them on another small round plate. Dip the rim of a martini glass in the lemon juice and then in the salt ensuring the rim of the glass is rimmed with the salt. Repeat with 5-7 more glasses.
Fill with warm soup and garnish with olive and crouton on a cocktail stick.