Browning the butter and rye flour added complex, nutty flavor that balanced the sweetness of these cookies. If you can’t find rye flour, substitute whole-wheat or graham flour. A touch of molasses (blackstrap, if available) deepened the flavor and added a welcome bitterness. While we preferred chopping our own bittersweet chocolate, high-quality chocolate chips are fine.
Don’t be afraid to cook the roux until it's quite dark—ours was the shade of peanut butter—and fragrant. It should smell nutty.