In a small non- reactive bowl combine all ingredients except radicchio. Whisk until emulsion is formed and reserve at room temperature.
Place quartered radicchio onto a hot grill or grill pan. Cook on each side for approximately 2 minutes per side. You are looking to achieve slightly wilted edges.
Remove from the grill and place onto a plate. Cover with a stainless steel bowl and allow steam to continue cooking radicchio for 5 minutes.
Drizzle vinaigrette over radicchio wedges and serve immediately.
Recipe courtesy of Alton Brown