Brie & caramelised leek wholemeal tart

1. Put the flour and a pinch of salt in a large bowl, add the 100g diced butter and use your fingertips to rub together until it resembles fine breadcrumbs. Add 3 tbsp cold water, then use a palette knife to draw the pastry together. When it starts to clump, bring it together with your hands, adding 1-2 tbsp more water if needed. (Alternatively, use a food processor.) Knead lightly into a disc. Cover and chill for at least 20 minutes.

2. Preheat the oven to 220˚C, gas mark 7. On a floured surface, roll out the pastry to 0.3cm thick and use to line a 25cm round fluted tart tin (about 2.5cm deep); let the excess pastry hang over the edge. Put on a baking tray and prick the base with a fork. Line with baking parchment, fill with baking beans, then bake for 20 minutes. Remove the parchment and beans; bake for 10-12 minutes, until golden and crisp. Leave to cool, then trim the overhanging pastry. Reduce the oven to 200˚C, gas mark 6.

3. Meanwhile, heat the remaining 20g butter and the oil in a pan. Add the leeks and a pinch of salt; cook over a low-medium heat for 25-30 minutes, stirring occasionally, until soft and turning golden. Add the vinegar and sugar, raise the heat a little, and cook for 3-4 minutes until slightly sticky. 

4. Use a balloon whisk to whisk the eggs in a large bowl, then whisk in the crème fraîche. Add the leeks, mustard, and a pinch of salt. Pour into the tart case, then lay the brie on top. Scatter over the thyme leaves. Bake in the centre of the oven for 30-35 minutes until set and light golden. Cool in the tin for 5 minutes, then remove. Scatter over the extra thyme leaves and serve warm, or cool completely on a wire rack.