Wedge Salad with Elegant Blue Cheese Dressing

½ pound crumbled blue cheese

¼ cup sour cream

⅓ cup buttermilk

½ cup mayonnaise

¼ cup red wine vinegar

1 tablespoon extra-virgin olive oil

1 ½ tablespoons white sugar

1 clove garlic

minced

ground black pepper to taste

1 head iceberg lettuce

cut into 8 wedges

2 roma tomatoes

diced

1 small red onion

thinly sliced

½ pound crumbled blue cheese