For the rhubarb, slice each stalk in half, down the middle, and place in a dish. Zest and squeeze the juice of half the orange, and cut open half the vanilla pod and scrape the seeds. Place the zest, juice, vanilla seeds, and pod in the dish with the 40g sugar and rhubarb. Toss to evenly cover the rhubarb and allow to sit for at least an hour.

For the pastry cream, combine the milk, sugar, zest, from the second half of the orange, and remaining vanilla seeds and pod. Bring the milk to a gentle simmer, and remove from the heat. Cover and allow to seep for at least 30 minutes.

Once the cream has infused long enough, whisk the egg yolk with the cornstarch, and pour in some of the milk mixture to thin it out a little. Bring the milk to a low boil and slowly pour into the cornstarch mixture, while whisking vigorously.

Return the whole mix to the pot and bring to a boil over a medium heat, while whisking the whole time. When you feel the mixture start to thicken, briefly remove from the heat and whisk, to prevent the egg from over cooking. Then return to the heat and bring to a boil. Once boiling, continue to cook for 10 seconds to ensure that the corn starch is cooked out.

Remove from the heat, and stir in 2-3 tbsp of the blood orange juice. Pour through a sieve onto a large piece of cling film. Wrap the pastry cream in the cling film to make a little parcel and allow to cool in the fridge. If you have extra juice, pour it over the rhubarb.

To make the danish dough, the method depends on which kind of yeast you are using. If fresh, add it to the cold milk; if active dry, warm the milk to 115°F (45°C) and dissolve the yeast in it first; if instant, mix in with the flour. Depending on your yeast, place the ingredients in the bowl in the following order: milk, egg, sugar, flour, salt, and butter (in small pieces).

Mix the ingredients together until they resemble a shaggy mass, and then turn out onto a lightly floured work surface. Knead the dough slowly for 2 minutes, just to get the ingredients combined and the butter worked in, then up the speed to fast for 8 minutes. Wrap the dough in cling film and allow to rest in the fridge for 20 minutes.

While the dough is resting, make the butter block. Wrap the butter in cling film, and pound with a rolling pin. Continue pounding the butter, and folding the edges over, until you can fold the butter and it doesn't crack. Shape the butter into a 20cm square and set aside at room temperature until the dough is ready.

To encase the butter, roll the dough out to a 20cm rectangle, on a well floured surface. Cut a cross into the dough and pull out the corners. Roll them out while keeping the middle slightly raised. Brush off any extra flour, and place the butter block in the middle.

Cover the butter with the dough flaps, one at a time, brushing off the extra flour, and pinch to completely seal.

To make the first turn, gently press the dough with a rolling pin to merge the layers together, and then roll out in one direction to 45 cm long. Fold the top third of the dough down, brush off the extra flour, and fold the bottom up to cover. You should have a rectangle of dough with three layers. Cover in cling film and allow to rest for 30 minutes. You can speed up the rest time with a brief turn in the fridge, but need to make sure that the butter stays soft.

For the second turn, roll the dough in the opposite direction as before (rolling the open ends out) and complete the turn as the first. Allow to rest for 30 minutes again.

Complete the third turn, same as the second, and allow to rest for 20 minutes.

Once the dough is ready, roll it out on a well floured surface to just larger than a 21 cm x 70 cm rectangle and then cut the edges of the dough to 21 cm x 70 cm. Cut the dough into 30 squares, 7 cm x 7 cm. Using a round cookie cutter, cut 15 circles from half the squares.

Remove the rhubarb from the dish and line up the stalks on a cutting board. Using the same circle cutter, cut circles of the rhubarb, using a small sharp knife if necessary. Cut 15 circles of rhubarb and the chop up any remaining rhubarb to top the scrap pieces.

Brush a little water around the edges of the full squares and top with the ones with the circles cut out. Pipe a bit of the cream in the middle and top with the circles of rhubarb.

For the scrap circles, pipe on a small mound of cream, and top with some of the chopped rhubarb.

Place all the danish on parchment lines trays and sprinkle with some turbinado sugar (demererra sugar) if you like. Cover the trays with upside down plastic bins, or loosely with cling film, and allow to proof for 1.5-2 hours, or until well puffed and you can start to see the layers.

While the danish are proving, preheat the oven to 340°F (170°C).

Bake the danish for 20 minutes, or until golden brown. rotating after 10 minutes if necessary.

Remove from the oven, and allow to cool on racks. If desired, make a simple glaze with water (or milk) and icing sugar, and drizzle over the top.