01 -
Preheat the oven to 425°F. Use a large sheet pan so the Brussels sprouts have room to roast in a single layer.
02 -
Trim the dry stem ends from the Brussels sprouts and remove any loose yellow leaves. Halve small sprouts and quarter large ones so they cook evenly.
03 -
Toss the sprouts with olive oil, garlic powder, salt, and pepper until evenly coated. Arrange them cut-side down on the sheet pan.
04 -
Roast for 20-25 minutes, turning once near the end, until the cut sides are browned and the outer leaves are crisp.
05 -
While the sprouts roast, stir together mayonnaise, Dijon mustard, olive oil, lemon juice, garlic, parsley, salt, and pepper. Chill until ready to serve.
06 -
Transfer the hot Brussels sprouts to a platter, sprinkle with extra parsley, and serve with the Dijon aioli for dipping.