Heat a large skillet, over high, for a few minutes; drops of water should skitter across the surface then evaporate quickly.
Set the pan lid and 1/2 cup water next to the stove.
Add enough oil to coat the bottom of the pan; around 3 to 4 tablespoons; add garlic and sizzle until fragrant and wisps of smoke rise from the oil; about 15 seconds.
Add brussels sprouts, sprinkle with salt and pepper, and stir to coat with oil.
Spread in an even layer, carefully add water and immediately cover.
Cook without stirring until the water has almost completely evaporated; 4 to 6 minutes.
After silent simmering, there will be loud popping sounds that quiet to a crackle.
Uncover, sprinkle with sugar and soy sauce; stir for 1 minute.
Sprinkle with red-pepper flakes and serve.
