Preheat oven to 450 degrees. Trim, and cut cauliflower into small florets; spread in a roasting pan or rimmed baking sheet. Drizzle with olive oil; season with coarse salt and ground pepper. Toss to combine. Roast, tossing once or twice, until cauliflower is golden brown and tender, 20 to 25 minutes.
In a small skillet, melt butter over medium heat. Cook garlic cloves, stirring often, until lightly browned, 2 to 3 minutes. Remove from heat. Add capers and caper juice. Pour over cauliflower, and toss to coat.