Rinse brussels sprouts in a colander, shaking out excess water. Trim the woody ends off the sprouts and remove any damaged outer leaves.
Cut the brussels sprouts into quarters, or halves if they're small. Place in a steamer basket.
Place the steamer basket over a pot of boiling water (about an inch of water; don't let it touch the basket. Cover, reduce heat, and steam about 10 minutes or until just fork-tender. Do NOT overcook.*
Heat olive oil in a large skillet, then add garlic. Stir and cook about 30 seconds, until fragrant.
Add the steamed brussels sprouts and cook 2-3 minutes, stirring and tossing occasionally. Sprinkle on the sugar and vinegar, stir well, and cook another 3-5 minutes or until the sprouts have some golden brown color on them.
Season with salt and pepper and remove from heat. Best served immediately.
*NOTE: You can prepare up to this step a day in advance. Rinse steamed sprouts with cold water, let cool, and store in fridge. When ready to serve, remove from fridge and proceed with the other steps.