Fill a large saucepan with water and bring to a boil. Salt the water so it tastes like seawater. Separately, create an ice bath by filling a large bowl or casserole dish with equal amounts of cold water and ice. You will "shock" or stop the cooking process with the ice bath. Add the Brussels sprouts to the boiling water. Cook until tender, but not too long or they will lose their bright green color, 2 to 3 minutes. Remove the sprouts from the water and shock them in the ice bath. Leave the Brussels sprouts in the ice bath until they are cool, then remove them from the ice bath and reserve for later use. In a large saute pan over medium-high heat, add the bacon pieces and cook until the fat renders and the bacon crisps, about 7 minutes. Add the onions to the pan and cook until softened, another 5 minutes. Add the butter, allow it to melt, and then add the apple slices and thyme sprigs. Toss to coat, cooking another minute or 2. Add the blanched Brussels sprouts. Season with salt and pepper, and cook until the sprouts are golden brown, another 8 to 10 minutes, stirring occasionally. Remove the thyme sprigs and discard. Drizzle half the Sherry-Dijon Vinaigrette onto the sprouts and toss. Serve the remaining vinaigrette alongside the sprouts.
Add the canola oil, olive oil, vinegar and mustard to a blender and blend until fully incorporated. Season with salt and pepper.