Potatoes Thermidor

Thermidor sauce is traditionally paired with lobster, but this recipe applies that same rich, sherry-spiked cream sauce to russet potatoes for an elegant side dish that feels far more indulgent than its ingredients suggest. Shallots sauteed in butter, a roux thickened with cream, sliced mushrooms, and dry sherry make up the sauce that gets poured over the cut potatoes before a final bake.

The roux needs 3-5 minutes of cooking before the cream goes in. This step cooks the raw flour taste out and ensures the sauce thickens properly. Mushrooms go into the hot cream sauce and cook for just a few minutes, long enough to soften but not so long they turn slimy.

Beaten egg yolks mixed with sherry get stirred quickly into the hot sauce at the very end. The residual heat thickens the yolks into a silky, rich finish. A gentle bake at low heat warms everything through without curdling the egg-enriched sauce.

Chef Tips

• Cook the roux (butter and flour) for the full 3-5 minutes, stirring constantly. Undercooked roux tastes pasty and the sauce won’t thicken properly.
• Temper the egg yolks by adding a spoonful of hot sauce to them first, then stirring the mixture back into the pan. Dumping cold yolks into hot cream scrambles them.
• Use dry sherry, not cooking sherry. Cooking sherry has added salt and preservatives that ruin the flavor.
• Bake at the low temperature as directed. The egg yolks need gentle heat or they’ll curdle and make the sauce grainy.

Variations

• Add a handful of grated Gruyere on top before baking for a golden, bubbly cheese crust.
• Use Yukon Gold potatoes for a creamier, more buttery base.
• Stir in cooked lobster or shrimp pieces to make this a main course with proper Thermidor credentials.