Step 1

Place beetroot in a pan of cold water and bring to the boil. Reduce heat to medium-low and simmer for 1 hour, topping with water if necessary, until tender. Drain. Refresh under cold water and leave to cool. Peel and coarsely grate. Set aside.

Step 2

Meanwhile, for the pastry, place flour, butter, thyme and a pinch salt in a food processor and whiz until the mixture resembles breadcrumbs. Add 1/4 cup (60ml) chilled water, then process until the mixture comes together in a ball. Enclose in plastic wrap and chill for 30 minutes. Lightly grease a 30cm loose-bottomed tart pan. On a lightly floured surface, roll out pastry to 5mm thick, then use to line the tart pan. Chill for 15 minutes.

Step 3

Preheat oven to 180°C. Line pastry with baking paper and fill with pastry weights or uncooked rice. Bake for 10 minutes. Remove the paper and weights, then bake for 5 minutes or until dry and pale golden.

Step 4

Heat the butter and oil in a frypan over medium heat. Add onions and 1 teaspoon salt, then cook, stirring occasionally, for 6-8 minutes until softened. Add beetroot, vinegar, thyme and sugar, then cook, stirring, for 5 minutes or until thickened and syrupy. Spread beetroot mixture over the tart base, then crumble over cheese.

Step 5

Whisk egg, cream and nutmeg together, then pour into tart case. Scatter with extra thyme. Bake for 35 minutes or until set.

Step 6

Meanwhile, combine creme fraiche, horseradish, Dijon, and lemon juice, then season. Keep chilled until ready to serve.

Step 7

Cut tart into slices and serve warm or cold with the horseradish cream.