How do I know when the cabbage wedges are done roasting?
Roast until the cut edges are deeply golden-brown and the outer leaves are caramelized. The wedges should be fork-tender and slightly charred at the edges, which concentrates the natural sweetness.
Can I make the Gruyère sauce ahead of time?
Yes. Prepare the sauce up to 2 days ahead and refrigerate in an airtight container. Reheat gently over low heat, stirring often, adding a splash of cream if it thickens too much.
What if I don't have hazelnuts?
Toasted walnuts, pecans, or almonds work well. For a different profile, try crispy bacon bits or breadcrumbs toasted in butter.
Can I use regular green cabbage instead of Savoy?
Yes, though roasting time may increase slightly. Savoy has thinner, more tender leaves that caramelize faster, but green cabbage will develop good color and sweetness with patience.
How do I prevent the sauce from breaking or becoming grainy?
Keep heat moderate when making the béchamel, stir in cheese slowly off heat, and add Dijon mustard last—its acidity helps stabilize the emulsion.