In a small bowl, whisk vinaigrette ingredients together until blended. Place spinach, cannellini beans and red onion in a large bowl. Add vinaigrette and toss.
Melt butter in a small skillet over medium heat. Add the pine nuts and stir until fragrant, about a minute, then add the prosciutto and stir constantly, separating the ribbons, until it is warmed through, about 2 more minutes. Remove from the heat and let this mixture cool slightly before adding it to the salad and tossing to combine. Taste and season with salt and pepper if needed.
Find it online: https://www.therightrecipe.org/archives/1948