Step 1

Arrange a rack in the middle of the oven and heat the oven to 425°F.

Step 2

Finely grate 2 garlic cloves onto a rimmed baking sheet. Trim 1/2-inch off the woody, dried-out bottom of the stems of 8 ounces broccoli and cut the core from 8 ounces cauliflower. Cut the florets into bite-sized pieces and place on the baking sheet. Cut the stems into bite-sized (1- to 1 1/4-inch) pieces and add to the baking sheet.

Step 3

Drizzle with 2 tablespoons olive oil, sprinkle with 3/4 teaspoon kosher salt, 1/4 teaspoon black pepper, and 1/4 teaspoon red pepper flakes if using. Toss until the broccoli and cauliflower are evenly coated and the garlic is evenly distributed. Spread out in an even layer.

Step 4

Roast, tossing halfway through, until tender and caramelized at the edges, 20 to 25 minutes total. Taste and season with more kosher salt as needed.