Roasted rhubarb brioche doughnuts

PASTRY CREAM

1. In a large bowl, whisk together the yolks, sugar and cornflour in a bowl. 
2. In a medium pot, warm the milk and vanilla paste until there is movement just around the edges of the milk - do not bring it to the boil. 
3. Remove the milk from the heat, and, whisking constantly, add half of the milk mixture into the egg and cornflour mixture to temper the egg yolks. Whisk briskly for 30 seconds. Transfer the milk-yolk mixture back to the pot, and return to a medium heat. Whisk constantly until very thick. 
4. Remove from the heat and whisk in the butter, mixing well until totally combined. Allow to stand for 5-10 minutes, whisking occasionally. 
5. Strain the pastry cream through a mesh sieve, and into a bowl. Cool to room temperature then place a piece of plastic wrap directly on the pastry cream to prevent a skin. Place in the fridge until completely cooled.

VANILLA SUGAR

1. In a small bowl, rub the vanilla bean paste into the sugar using your finger tips. Spread out on a plate to dry at room temp. When you are ready to use, break up using your fingers. Pass through a mesh sieve if required to remove any lumps.

ROASTED RHUBARB

1. Preheat oven to 180˚c / 350˚f. Toss together the rhubarb, vanilla paste and sugar in a bowl. Transfer to a baking tray and roast for 15-20 minutes, until the rhubarb is soft and syrupy. Allow to cool slightly then either transfer to a blender or food processor and puree, or mash well with a potato masher. Allow to cool completely.

DOUGHNUTS

1. In a small bowl, combine the lukewarm milk, yeast, and 1 Tbsp of the sugar. Stir to combine, and leave for 5 minutes until foamy.
2. In the bowl of a stand mixer, combine the flour, remaining sugar, and salt. Mix on low using the dough hook.
3. Add the yeast and eggs to the dry ingredients, and mix on low until the dough forms a sticky ball. Increase the speed of the mixer and knead for another 5 minutes, stopping occasionally to clear the dough hook of dough. 
4. With the mixer on medium, add the butter a cube at a time, waiting until it is fully incorporated before adding the next piece. This process should take 12-15 minutes. Once the butter is fully incorporated, knead for a further two minutes, until the dough is soft and elastic, and passes the "window pane" test. This is where the dough will stretch and become transparent when stretched out. If it breaks, continue to knead until it reaches this stage. 
5. Cover the bowl with a wet kitchen towel, and allow to prove until doubled in size, 45-90 minutes depending on the conditions in your kitchen. 
6. Turn the dough out onto a well floured surface. Roll into a circle that is about 2.5cm thick (1 inch). Leave to sit for 5 minutes to allow the dough to relax.
7. Cut out circle shapes using a cookie cutter approximately 2.5 inches (6cm) in diameter. Place the cut doughnuts on a baking tray lined with parchment paper.
8. Leave the doughnuts to proof for a further 20 minutes. When you poke them lightly with your finger, it should leave a small indentation that springs back. 
9. While the doughnuts are proofing, heat the oil in a large heavy-bottomed pot (cast iron works great). Heat the oil to 175-180˚c / 340-350˚f. 
10. Once the oil has come to temperature, test it with a few scraps of dough. Gently lower the doughnuts, two at a time, into the hot oil. Cook for 1 ½ - 2 minutes on each side until golden brown. Remove from the oil using a slotted spoon and place on a cooling rack. Allow to cool for 30 seconds before tossing in the vanilla sugar. Repeat the process with the rest of the doughnuts. Once the doughnuts are cool, poke a hole in them using a chopstick, and widen the hole using your finger.

ASSEMBLY

1. Fill a piping bag fitted with a medium-sized round tip with the pastry cream. Fill a second bag with the rhubarb puree. Carefully fill the cavity of the doughnut halfway with rhubarb puree, then follow with the pastry cream, as full as the doughnut will allow you - you can usually feel when they are full. When you pull away the piping bag, a little of the pastry cream should ooze out. Top each with a small blob of the rhubarb.
2. Serve immediately. Best eaten on the day that they are made.