Cut butter into four or five pieces and cook butter in a small heavy saucepan over medium heat, stirring frequently, until it has a nutty fragrance and flecks on bottom of pan turn a light brown, anywhere from 4 to 7 minutes. It helps to frequently scrape the solids off the bottom of the pan in the last couple minutes to ensure even browning. Transfer butter to a bowl and chill until just firm, about 1 hour in refrigerator or ½ hour in freezer.