Heat vegetable oil in a skillet over medium-high and add sausage. Cook until browned, about 5 minutes.
STEP 2
Reduce heat to medium, add onions and salt, cook until soft, about 5 minutes.
STEP 3
Stir in butter, then add flour. Cook for 2 minutes. Add diced apple, cook for another 1 minute.
STEP 4
Pour in chicken broth, raise heat to high, scraping fond. Add milk and bring to a simmer. Simmer for 15 minutes.
STEP 5
Combine egg, cider, creme fraiche, thyme, 2 tablespoons green onions, 1 teaspoon salt, and baking powder in a bowl. Whisk well. Add 1 cup flour and mix until combined.
STEP 6
Stir gravy and adjust seasoning. Add pepper, cayenne, green onions, and vinegar.
STEP 7
Transfer rounded teaspoons of dumpling batter onto the simmering gravy.
STEP 8
Cover and cook, untouched, until dumplings are puffed and floating, 5-6 minutes. Serve topped with green onions.