Roll out the puff pastry on a lightly-floured surface and cut out a 28cm circle. Chill in the fridge.
In a large bowl, toss the pears with the lemon juice and 25g muscovado sugar.
Gently melt the butter in a 24cm oven-proof frying pan, then add the remaining 100g sugar and the vanilla seeds and melt over a medium-low heat. Shake the pan gently, but do not stir. Arrange the pears on top of the caramel in a spiral pattern. Cover with the pastry circle, tucking the edges inside the pan around the pears. Transfer the tarte tatin in the pan to the oven and bake for 30 mins, until golden brown and puffed up.
Remove from the oven and cool for 10 mins. Using a palette knife, loosen the pastry from the edge of the pan. Place a serving plate over the top and carefully flip the pan over to remove the tarte tatin. Slice and serve warm.
Nutritional information per portion
This nutritional information is only a guide and is based on 2,000 calories per day. For more information on eating a healthy diet, please visit the Food Standards Agency website.
Guideline Daily Amount for 2,000 calories per day are: 70g fat, 20g saturated fat, 90g sugar, 6g salt.