To make the sauce, combine fish sauce, lime juice, sugar and water in a bowl.
Whisk until thoroughly combined.
Add chillies and garlic and stir to combine.
Leave to rest for at least 15 minutes so that the flavors can develop.
To make the fritters, combine sweet potato, shrimp, scallions, fish sauce, black pepper and salt.
Mix until thoroughly combined.
Add flour, egg and baking powder.
Mix well until thoroughly combined and the batter starts to stick together.
Using approximately ½ cup of batter for each fritter, form into 10-12 fritters.
Heat a shallow skillet with enough oil for shallow frying, about 1” of oil.
Place fritters in the hot oil and cook on medium heat until fritters are golden brown and a little crispy on each side, approximately 4 minutes on each side.