Step 1Cook the bacon strips over medium heat until the fat is rendered and the strips are crisp, about 10 minutes. Drain the bacon on paper towels, reserving 3 tablespoons bacon grease.
Step 2Remove any wilted outer leaves from the radicchio and slice it lengthwise into eight wedges. Trim the top off the fennel, halve it lengthwise, then slice it crosswise into half-inch strips, discarding the core. Core the apples and cut each into 8 wedges.
Step 3Whisk together the shallots, thyme, rosemary, maple syrup, vinegar, bacon grease and olive oil. Season with one-half teaspoon salt and a grind of black pepper, or to taste. This makes about 1 cup vinaigrette.
Step 4Brush the apple wedges with a little of the vinaigrette and place them on an oiled grill heated over medium-high heat. Grill the wedges for about 2 minutes on each side, until slightly softened with defined grill marks. Remove and reserve in a warm place. Do the same with the fennel and radicchio.
Step 5Divide the apple, fennel and radicchio among 4 plates. Crumble the blue cheese over the salads, and sprinkle over the bacon. Drizzle 1 to 2 teaspoons of the remaining vinaigrette over each salad. Serve immediately.