Melt butter in a nonstick skillet over medium-high heat. Stir in onions, salt and pepper. Continue cooking, stirring occasionally, for 5 minutes or until onions begin to soften.
Stir in sugar. Cook, stirring occasionally and scraping brown bits off bottom of pan, 20-25 minutes or until onions are golden brown. (Reduce heat, if necessary, to keep from burning.) Stir in parsley; place onion mixture into bowl.
Heat oven to 400 degrees.
Place bread slices onto baking sheet. Divide onion mixture evenly among bread slices. Top each with blue cheese. Bake 5-7 minutes or until bread is toasted and cheese is melted.
PRO TIP: Garnish with bacon bits or replace bleu cheese with goat cheese