Pound aromatics: Add garlic, coriander root, and black peppercorns to a mortar and pound until coarse and fragrant.
Make crispy garlic: Heat oil in a pan over medium heat. Add the pounded garlic mixture and fry gently, stirring often, until lightly golden. Add sliced chili, salt, sugar, and rosdee seasoning powder, stir briefly, then remove from heat. Set aside.
Coat shrimp: Pat shrimp dry. Toss with tempura flour until lightly coated, shaking off excess.
Fry shrimp: Heat oil for deep-frying (or pan-fry) in a pan over medium heat. Fry shrimp until golden and crispy, turning once. Do not overcrowd the pan.
Drain: Remove shrimp and drain on a rack or paper towels.
Serve: Arrange shrimp on a plate and spoon the crispy garlic mixture over the top. Serve immediately.