Lightly coat a cookie sheet with cooking spray; set aside.
Place butter in a 2-quart microwave-safe bowl. Microwave, covered, at HIGH 1 1/2 to 2 minutes or until butter melts. Stir in sugar, water, and corn syrup. Microwave at HIGH 1 minute. Stir and microwave 3 more minutes. Stir well. Cover and microwave 1 more minute.
Uncover and stir in sesame seeds. Microwave, uncovered, at HIGH 2 to 3 minutes or until candy is light caramel in color. Pour candy onto prepared cookie sheet, spreading to 1/8" thickness. Cool completely on cookie sheet on a wire rack; break candy into pieces. Store in an airtight container.