French Onion Tart (Tarte à l'Oignon) Recipe

About This Recipe

The French onion tart from Alsace is one of those dishes where patience transforms something humble (an onion) into something extraordinary. The onions must be caramelised over very low heat for 40–50 minutes until golden, sweet and jammy. Combined with cream and eggs, they become a silky, intensely flavoured custard in a crisp, buttery pastry shell.

Ingredients

Serves 6

• 200 gplain flour(for pastry)
• 100 gcold unsalted butter(cubed, for pastry)
• 1 egg yolkegg yolk(for pastry)
• 2 tbspcold water
• 1 kgwhite onions(thinly sliced (about 5 large))
• 50 gunsalted butter(for caramelising)
• 1 tspcaster sugar
• 3eggs
• 200 mldouble cream
• 0.5 tspground nutmeg
• 1 tspsalt

Instructions

1. 1

   Make the pastry

   Rub butter into flour until fine crumbs. Mix in egg yolk and cold water. Form into a disc, wrap and refrigerate 30 minutes. Roll and line a 23cm tart tin. Blind bake at 190°C for 15 minutes with baking beans, then 5 more minutes uncovered.

2. 2

   Caramelise the onions

   Melt butter in a large pan over very low heat. Add onions, salt and sugar. Cook, stirring every 5 minutes, for 45–50 minutes until deep golden, very soft and jammy. This cannot be rushed.

   The Maillard reaction that creates the caramelised flavour needs time at low heat. High heat burns the edges before the inside softens.

3. 3

   Make the custard and bake

   Whisk eggs, cream, nutmeg and salt. Stir in caramelised onions. Pour into the blind-baked shell. Bake at 180°C for 30–35 minutes until set with a slight wobble. Cool 10 minutes before slicing.

Variations

• •

  With Gruyère: scatter 60g grated Gruyère over the onions before pouring the custard.

• •

  With thyme: add 1 tsp fresh thyme leaves to the caramelised onions.

Storage

Keep refrigerated for 3 days. Serve at room temperature or warm in a 160°C oven for 10 minutes.

Frequently Asked Questions