Bring a large pot of water to a boil. Add 1 tablespoon of sugar and the corn to the pot. Turn off the heat and cook for 3-4 minutes. Remove the corn and allow to cool to room temperature.
Remove the kernels from the cob using a sharp knife by cutting downward in a large bowl.
Add the black-eyed peas, spinach and onion to the corn. Toss to combine.
In a small bowl, whisk together the buttermilk, mayonnaise, mustard, vinegar, garlic powder, cayenne, salt and pepper until smooth.
Pour the dressing over the salad and toss to combine.