Danielle Kartes' Coconut CustardMacaroons

"Instead of the straightforward sweet, coconutty chew of classic macaroons, these have a more rounded richness, and a welcome savory oomph. Butter has an amplifying effect—the cookies don’t just taste better because butter inherently tastes good, but because it turns to browned butter in the oven, and mingles with sugars and salt to become caramel. All of these flavors are swim along quite happily with coconut. At the same time, the butter and egg yolk help the pointy outer edges of the macaroon brown and crisp up, while the inside stays soft and custardy. Adapted from Danielle Kartes of the blog and cookbook Rustic Joyful Food...."