Gestoofde witlof: tender Belgian endives gently braised in butter and lemon juice, then baked in a silky nutmeg béchamel sauce under a golden, bubbly blanket of grated mature Dutch Gouda.
Trim the base of the endives and remove any damaged outer leaves, cutting a small cone out of the core to reduce bitterness. Halve lengthwise. Melt 20g butter in a wide lidded skillet, add the endive halves cut-side down, lemon juice, sugar, and 50ml water. Cover and braise on low heat for 15 minutes until tender.
In a saucepan, melt the remaining 20g butter, whisk in the flour, and cook for 1 minute. Gradually whisk in the milk, simmering gently until a thick, smooth sauce forms. Season with grated nutmeg, salt, and white pepper, then stir in half of the grated Gouda until melted.
Transfer the braised endives into an ovenproof baking dish, arranging them neatly cut-side up. Spoon the warm cheese sauce evenly over the endives.
Top with the remaining grated Gouda. Bake at 200°C (180°C fan) for 18 to 20 minutes until the gratin is bubbling and the top is richly bronzed and crispy.