Instructions:

Preheat the oven to 350°F. Soak potato slices in cold water to eliminate starch. This step can be done a few hours in advance.

In a skillet, melt 4 tbsp butter and 4 tbsp olive oil over medium-high heat. Add onions and cook until caramelized. Sprinkle flour over the onions.

Pour in chicken stock and milk, stirring until the mixture thickens. Season to taste, then stir in cheese and chives. Remove from heat once the cheese melts.

Grease a casserole dish. Drain the potatoes and layer them, followed by the cheese sauce. Repeat the layers.