The chocolate flavor in these brownies comes from a mixture of unsweetened and bittersweet chocolate, melted together over simmering water, into which nearly half a pound of melted butter is mixed. I used TCHO chocolate for both (the bittersweet was 66%) as that’s what Flour uses; I bought the chocolate at the Sur La Table store in the Natick Mall, but it’s also available by mail order from the usual sources.