Preheat your oven to 350°F (175°C). Cut the rye bread into ½ to ¾ inch cubes and arrange them on a baking sheet, toast for 8-10 minutes.

In a skillet, heat olive oil and sauté onions and celery for 3-4 minutes until soft. Add garlic and sage; cook for 1 more minute. Brown sausage, then fold in chopped chestnuts.

In a mixing bowl, combine sausage mixture with toasted bread cubes. Beat the egg and mix in. Gradually add broth until moist but not soggy.

Grease a casserole dish, spoon in the mixture, and bake for 35-40 minutes until golden brown. Garnish with parsley if desired.