Coleslaw With Grapes and Spinach

1 cup mayonnaise

½ cup white sugar

3 tablespoons vinegar

salt and ground black pepper to taste

½ head cabbage, thinly sliced

2 heads broccoli, trimmed and cut into thin strips

1 red onion, thinly sliced

½ (10 ounce) bag fresh spinach leaves, thinly sliced

1 pound seedless red grapes, quartered

Whisk mayonnaise, sugar, vinegar, salt, and black pepper in a large salad bowl; fold in cabbage, broccoli, red onion, spinach, and red grapes. Stir to coat with dressing.