1 Pour onto a baking sheet, and place on center oven rack. 2  Roast in the preheated oven for 30 to 45 minutes, shaking pan every 5 to 7 minutes for even browning. 3  Reduce heat when necessary to prevent burning. 4  Brussels sprouts should be darkest brown, almost black, when done. Pour onto a baking sheet, and place on center oven rack. 2  Roast in the preheated oven for 30 to 45 minutes, shaking pan every 5 to 7 minutes for even browning. 3  Reduce heat when necessary to prevent burning. 4  Brussels sprouts should be darkest brown, almost black, when done.