Sprinkle a little flour over the dough and on a clean worktop, and pat the ball into a flat round about 1 inch thick. Sprinkle over a little more flour, then wrap the dough in plastic wrap and pop it into the refrigerator to rest for at least 30 minutes. Get yourself a 9 1/2-inch nonstick loose-bottomed tart or quiche pan (approx. 1 1/4 inch deep) and, using a splash of vegetable oil on a paper towel, lightly oil the inside.
While the crust is in the refrigerator for 30 minutes, pierce your sweet potatoes with a fork, lay them on a sheet pan, and pop them into the oven-they’ll need about 50 minutes to an hour, until they’re soft and cooked through. When they’re ready, take them out of the oven and turn the temperature down to 350°F.
While the potatoes are in the oven, dust a clean surface and a rolling pin with flour, then carefully roll out your pastry, turning it every so often, until its just under 1/4-inch thick. Carefully roll your pastry around the rolling pin, then unroll it carefully over your oiled pan. Ease the pastry into the pan, making sure you push it into all the sides. Trim off any excess by running a knife along the top of the pie crust, then prick the base of the pie crust all over with a fork and pop it into the freezer for 30 minutes.
Get yourself a large square piece of parchment paper, scrunch it up, then unwrap it and use it to line your pie crust, pushing it right into the sides. Fill the pie crust right up to the top with rice, and bake blind for 10 minutes in your preheated oven. Take the pie crust out, carefully remove the rice and parchment paper (you can save the rice to you for blind baking another time), then return the crust to the oven to cook for a further 10 minutes, until it’s firm and almost cookie like. Let cool.
While the pie crust is in the oven, peel the skins from the roasted sweet potatoes and discard. Put the flesh into a large bowl and mash it up. Melt your butter in a saucepan on a low heat and add it to the sweet potato with the sugar, flour, nutmeg, a large pinch of cinnamon, and the vanilla extract. Whisk 2 eggs in a separate bowl, pour them into the mixture, then mash everything together until completely combined.
Spoon your sweet potato mixture into the cooled pie crust, and use a fork or spoon to spread it out evenly. Dust a clean surface and a rolling pin with flour and roll out your leftover pastry (plus any bits that you trimmed off the sides). Cut it into long strips, a bit longer than the width of your pie. Drape these strips over the top, crisscrossing them as you go so you get a nice lattice design on the top. Tidy up the sides, then beat your remaining egg and brush it over the pastry. Put the pie into the oven and bake for 45 to 50 minutes, until gorgeous and golden.
Make your Clementine cream just before serving by whipping the cream, Clementine zest and juice, and sugar together until you’ve got soft peaks. Take your pie out of the oven and let it cool for about 25 minutes before serving with the clementine cream. Lovely with a few sliced of clementine on the side.
PS: If you’re looking for something different to make at Christmas, try making individual ones instead of your regular mince pies.