Marinate 380 grams shrimp with 1 tablespoon potato starch, 2 teaspoons fish sauce , ¼ teaspoon salt, and 1¼ teaspoon ground white pepper.
To cut the 200 grams pineapple, trim off both ends and slice it into quarters lengthwise. Then, remove the core from the center of one-quarter of the pineapple and cut the quarter in half lengthwise. Slice the skin from the pineapple and cut each segment into bite-sized pieces (I used an oblique cut).
Heat a frying pan over high heat until hot. Add 1 tablespoon vegetable oil and 7 grams garlic and swirl it around the pan.
Add the shrimp and quickly spread it into a single layer, allowing it to cook through on one side.
Toss the shrimp in the pan to flip them over. If you missed any, flip the remaining ones by hand.
When the shrimp is almost (but not fully) cooked, add 200 grams pineapple, and then stir-fry the mixture until the shrimp is fully cooked and the pineapple is just starting to brown around the edges (another minute or so).
Add 35 grams scallion and toss to distribute and serve the pineapple shrimp immediately.