In this traditional Vietnamese appetizer, freshly pureed shrimp paste is shaped around sticks of steamed sugarcane, and then grilled until lightly charred.
In a small skillet, heat oil over low heat. Add onion and shallots; cook, stirring occasionally, until translucent, 6 to 7 minutes.
In a food processor, pulse shrimp to a textured paste, about 20 pulses. Transfer to a bowl; add onion mixture, fish sauce, salt, sugar, garlic, pepper, cornstarch, paprika, baking powder, and scallions. Stir to combine; cover and refrigerate for 30 minutes.
Lightly brush a baking sheet with oil. Dampen your hands slightly with cold water and shape 2 tablespoons shrimp paste into a ball. Hold shrimp paste in one hand and press a piece of sugarcane into it, enclosing center of sugarcane but leaving about 1 1/2 inches exposed at top and bottom. Set aside on prepared baking sheet. Repeat, using all shrimp paste and sugarcane.
Brush a bamboo or metal steamer basket with oil; place over boiling water in a wide saucepan or wok. Steam sugarcane sticks, covered, until shrimp is opaque, 4 to 5 minutes. They may be prepared up to this point 6 hours in advance; refrigerate until about 15 minutes before ready to serve.
Brush a grill or grill pan with oil; heat until hot. Grill sticks until lightly charred all over, 5 to 8 minutes. Brush with Scallion Oil, if desired, and serve.