New potato and onion tarte tatin with crispy capers and hazelnuts

Method

1. Put the potatoes into boiling, salted water and cook for 15 minutes or until almost tender. When cool enough to handle, trim off the rounded tops and bottoms (discard or keep to add to soup), then slice into 2cm discs.
2. In a large, heavy-based frying pan, melt 30g of the butter and gently cook the onions, stirring occasionally, until softened completely (about 10 minutes). Turn up the heat, allow them to colour a little, stir through the garlic and cook for a couple more minutes, then set aside.
3. Clean the pan well, making sure it’s not greasy, then put it back on the hob and add the sugar. Cook over a very low heat to melt the sugar (don’t stir – it will take 10-12 minutes), then increase the heat slightly and swirl the pan until the sugar turns into a deep red-brown caramel. Remove it from the heat, immediately stir in the rest of the butter and the lemon juice (be careful – it may spit) and, once mixed, leave to cool fully. If the caramel goes lumpy, put it back over a low heat until melted.
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4. Heat the oven to 200°C/180°C fan/gas 6. Mix the mascarpone with the lemon zest and basil, then season generously. Push each potato piece into the caramel on the base of the pan, packing them in as tightly as you can. Scatter the onions on top, filling any gaps, then spoon the mascarpone all over in small dollops.
5. Roll out the pastry to the thickness of a £1 coin and trim it into a circle a little bigger than the top of the pan. Lay it over the mascarpone, tucking it in at the edges, then bake for 35 minutes or until puffed and golden.
6. While the tart is cooking, make the garnish. Heat the oil until shimmering in a frying pan and line a plate with kitchen paper. Add the capers to the pan and cook, stirring occasionally, for 1-2 minutes, then add the hazelnuts and cook for 2-3 minutes more until the nuts are golden and the capers dark and crisp. Drain on kitchen paper.
7. Remove the tart from the oven and leave for a minute. Put an upturned plate over the pan, then invert in one move to remove the tart onto the plate (replace any potatoes that stay stuck to the pan). Scatter with some of the crispy capers and nuts, then serve with the rest of the garnish on the side and a green salad.