Add butter to the skillet and cook over medium-high heat, stirring frequently, until it turns golden brown and toasty, about 1 to 2 minutes. Add garlic, red-pepper flakes, 1½ teaspoons salt, and a few grinds of black pepper, adjusting the heat if necessary to prevent burning. Stir in the tomatoes and 3 tablespoons of water, cooking and shaking the pan occasionally until the tomatoes soften and the liquid slightly thickens, about 4 to 6 minutes. Smash the tomatoes as they burst to help them cook down.