In a medium skillet, cook bacon until it’s browned and crispy, drain on paper towels, reserving drippings.
Add thinly sliced shallot to the bacon drippings and saute over medium-low heat until tender. Remove from heat, whisk in olive oil, apple cider vinegar, brown sugar, pinch of cayenne, and salt & pepper.
Adjust the sweet/tart flavor by adding more sugar or vinegar to taste.
Serve warm. Return crispy bacon to the salad or the dressing just before serving.