Make the puree:
Saute the scallion in the olive oil over medium heat for 3 minutes; stir in the peppers, and season with salt. Cook for 3 minutes over high heat; add the sugar. Cook for 2 more minutes; pour in the vinegar and cornstarch, and bring to a boil. Fold in the tomatoes. Simmer the sauce for 15 minutes; stir in the parsley, adjust the salt, and keep warm.
Make the blossoms:
Combine the flour, yeast, and salt in a medium bowl; whisk in the beer. Set aside to rest for 30 minutes. Whip the egg whites with a pinch of salt in a clean bowl until they form soft peaks; fold them gently into the batter.
Heat the olive oil to 350° in a deep, wide pan. Dip a few blossoms at a time into the batter; fry until golden and crisp. Remove with a slotted spoon; blot dry on paper towels. Continue with the remaining blossoms. Serve hot, with the puree.