We started with our vanilla doughnut clusters, made with 6 doughnut holes fused together. We coated the tops with a glaze made with cold brewed coffee, instant coffee, powdered sugar, and salt. Finally we sprinkled our brown butter streusel over the doughnuts. The little nuggets of streusel stuck to to the glaze and filled in the nooks in the clusters. The combination of doughnut, coffee, and rich, sandy streusel became the ultimate exploration of coffee cake with the coffee on the cake.