To win the Best Hat competition at Lee Park & Arlington Hall Conservancy’s annual Day at the Races, on May 6, you’ll need a spectacular topper. So you need to seek out milliner Cassie MacGregor, founder of The House of MacGregor in Oak Cliff. MacGregor has been making derby hats since 2004 and has become a go-to for her whimsical designs. For 2017, she says it’s all about the three Bs. “The hats keep getting bigger and brighter every year,” she says, “and we are known for our bows.” Plan ahead for next year. MacGregor accepts custom orders (bring in your dress, and she’ll match it) through April 1. Styles range in price from $215 to $495. If you missed the cutoff, don’t worry. She has plenty of pre-made styles to choose from.