Turn oven to 425 degrees. Place Brussels sprouts and pancetta on baking sheet. Drizzle with olive oil. Sprinkle with salt and pepper. Toss together with your hands. (Your hands are the secret ingredient here, don’t you think?) Roast sprouts, gently stirring every 15 minutes, until deep golden brown roasty spots appear, 30-45 minutes. Remove from oven and place into mixing bowl. Add raisins.
In small saucepan over medium heat, melt butter. Add cashews. Stir frequently, keeping a close eye not to burn butter. Heat until foamy, the cashews have deepened in color, and the milk solids in the butter have turned toasty brown. (The more gentle your heat, and the longer you take to achieve this, the more flavorful the butter will become without risk of burning. Your exercise of patience in this step will be rewarded.)
Remove buttered nuts from heat and allow to cool slightly. Stir in balsamic vinegar. Pour over Brussels sprouts in bowl and gently stir. Adjust salt and pepper to taste.
Belly Restaurant serves this salad piled into endive spears, which is lovely. Sticks Forks Fingers is a big advocate of eating with our fingers!