Put the spinach in a large salad bowl and add the cut sections of grapefruit and oranges.
Whisk together the dressing ingredients in a small mason jar or bowl. Pour the dressing over the spinach and toss to coat.
Then make the nuts: over medium heat, in a small, non-stick pan, add the butter and sugar. Stir until the butter is melted.
Then add almonds (or the nuts you choose) and toss in the butter/sugar mixture. Toast the nuts for about 3 minutes, stirring occasionally, until they begin to brown. Stir in the rosemary and cayenne and stir just a few seconds to release the smell.
Remove the nuts from the heat and season with salt and pepper, to taste.
Sprinkle the nuts on the salad while still warm and serve.