In a bowl, whisk the egg, cornstarch, annatto, flour, water, fish sauce, salt and pepper until smooth and homogenous.
Add the squash, shallots and scallion to the mixture and mix.
In a large pan, heat about 2 inches of oil to a temperature of 350 F / 170 C.
Place about 2 to 3 tablespoons of the mixture on a skimmer, add 1 or 2 shrimps on it and lightly press.
Quickly slide the mixture into the hot oil and fry for about 3 minutes on each side or until the fritter is golden and crisp.
Remove from pan and drain on a rack placed on a baking sheet.
Serve hot with a spicy vinegar sauce.
In a large bowl, combine the vinegar, Thai red pepper, onion and garlic. Season with salt and pepper to taste.
