I made Nigella's Nectarine And Blueberry Galette from the Express book. It looked wonderful but sadly the pastry underneath was not cooked. I cooked it some more until the pastry on top was starting to burn but there was still uncooked pastry in the centre underneath. Please can you suggest how I perfect this. Many thanks.
Nigella's Nectarine And Blueberry Galette (from Nigella Express) is a tart made with a sheet of ready rolled store bought puff pastry. This pastry is 2-3mm (about 1/32 inch) thick so if you bought a block of puff pastry and rolled it out yourself then it could be that the pastry was rolled out a little too thick and so will not bake as quickly on the base.
Puff pastry also relies on a very hot oven in the initial stages of baking, to help the layers of pstry to rise and for the base to become crisp. Make sure that your oven is properly preheated to 220c/450F and that you bake the tart in the upper half of the oven. If you have two baking sheets that are the same size then it may also help to preheat one baking sheet in the oven then sit the baking sheet holding the tart on top of this sheet, as this will help the base of the tart to cook faster. Also line the baking sheet with a thin liner, such as baking parchment (parchment paper) or Bake-O-Glide. Thicker silicone mats could take longer to heat up and again could contribute to an undercooked base.
Finally, the blueberries and nectrines let out a fair amount of juice as they cook and the base of the tart will absorb some of these juices. This means that the base will cook through but never be fully crisp, though the edges of the tart should rise and become crisp.