In medium-sized frying pan, melt butter over medium heat and sauté onions until cooked through, several minutes.
In a large pot or Dutch oven over low heat, stir together canned pumpkin, chicken stock, half ‘n half, molasses, pumpkin pie spice, cayenne pepper, and salt. Let simmer on stove for 10-15 minutes, stirring occasionally.
While soup is simmering, cook bacon over medium-high heat until crispy. Remove to paper towels to drain, then crumble into bite-sized pieces.
Serve soup hot with blue cheese and bacon crumbles on top.