For the Cranberry Vinaigrette
Simmer cranberries, sugar, onion and rosemary with 1/2 cup water until cranberries “pop”, about 20 minutes.
Remove from heat and cool to room temperature. Whisk in Dijon mustard, then slowly whisk in oil. Season to taste.
For the Salad
Preheat grill on high heat. Core apples and cut into 1/4 inch slices (do not peel.) Cut fennel into slices of the same thickness (leave core in) and toss apples and fennel in oil.
Grill apples and fennel until lightly charred on both sides, but still crunchy, about 4 minutes in total.
To serve, arrange radicchio leaves on a platter and arrange apples and fennel over. Spoon cranberry vinaigrette over and serve.