This may sound a bit wacky, but it really is delicious. A pastry chef at The Ivy introduced me to it years ago and it stayed on the menu for ages.
200g ready-made, all-butter puff pastry
Plain flour, for dusting
300g caster sugar
2tsp fennel seeds
2tsp finely chopped dill (if there is no fern on the fennel)
Icing sugar, for dusting
200g crème fraîche
Roll out the pastry on a floured table to about 3mm thick. Cut the pastry into four 13cm discs and prick them all over with a fork. Leave to rest in the fridge for 1 hour.
Meantime, prepare the topping. Trim the fennel bulbs if necessary. If there is any fern on the fennel, chop it finely and put it to one side. Put the bulbs whole into a saucepan with the sugar and fennel seeds. Cover with water, bring to the boil and simmer gently for about 1 hour, until the fennel is soft to the point of a knife. Remove the bulbs from the cooking syrup, setting both aside. Preheat the oven to 200C/gas mark 6.
Place the pastry discs on a baking tray and cover with a wire cooling rack to stop them rising while cooking. Bake for 7 minutes, then turn the discs over and cook for a further 4 minutes with the rack in place. Remove from the oven and set aside.
Strain 500ml of the cooking syrup f through a fine-meshed sieve into a clean pan. Bring to the boil, lower to a simmer and cook until it has reduced to around 4 or 5 spoonfuls in volume. Remove from the heat and leave to cool a little before adding the chopped fennel fern or dill.
Cut the fennel bulbs lengthways into 5mm slices. To assemble the tarts, arrange the fennel slices on the puff pastry discs in a circular pattern, ensuring the fennel goes to the edges of the pastry.
Dust with icing sugar and bake for 7-8 minutes until golden (cover the tarts with foil if they begin to colour too rapidly). To serve, spoon the syrup around the tarts and top with a dollop of crème fraîche.