Smooth, lump-free potato au gratin
A velvety au gratin relies on even slicing, a well-made sauce, and gentle handling. Use a stable cheese like Gruyère or cheddar that melts smoothly, and a béchamel-style base to bind everything together without lumps.
Make the sauce carefully:
- Start with a roux: melt butter, whisk in flour, and cook briefly.
- Gradually whisk in warm milk or cream to avoid lumps.
- Stir until smooth and thickened, then add grated cheese off heat to prevent separation.
Assembly and baking:
- Layer uniformly thin potato slices in a buttered dish and season each layer lightly.
- Pour the smooth cheese sauce over the potatoes and press down to remove trapped air.
- Cover and bake until tender; uncover to brown the top.
Tips to prevent lumps:
- Warm the milk before adding to the roux.
- Whisk constantly when combining roux and liquid.
- Grate cheese finely and add it slowly off the heat to avoid graininess.
Rest before serving so the sauce sets slightly for cleaner slices. The end result should be creamy, cohesive, and finished with a golden crust.