Add yeast, milk and 1 tbsp of the sugar in a big bowl, cover and let sit for 10 min to bloom.
Then add the rest of the sugar, egg, flour, salt and cardamom, mix this with a stand mixer or by hand until incorporated.
When a dough has formed add the butter in cubes and mix continuously. Continue mixing for about 10 min until the dough is elastic.
Now let this rise for 2 hours in room temp. In the meantime make your filling by combining all ingredients in a bowl and set aside.
Next make the rhubarb compote by combining all ingredients in a saucepan and cook on medium high heat while stirring constantly, when thickened take of the heat.
Place in a bowl and put in the fridge to cool.
Lastly make the vanilla pastry cream by warming up milk, vanilla paste and cardamom on low heat. Meanwhile vigorously whisk the yolks, sugar, cornstarch , all purpose flour until pale and fluffy.
Add the warm milk to the egg mixture one 1/4 cup at a time. Transfer back to the stove and whisk on low heat until smooth pastry texture. Pour in a bowl and refrigerate.
When done resting place the proofed dough on a floured surface and roll out to a rectangular shape, you’re filling.
Fold over the short side of the dough to the other and use a pizza slicer to cut 1 cm thick stripes of dough.
Twist a stripe of dough and shape it like a bun.
Place on parchment paper and press the middle down using a small glass making a little well in the middle we’re you now are going to pipe the vanilla pastry cream and follow up with the rhubarb compote ( be careful not to overfill the buns ).
Now let the dough rest for another 10-15 min before baking in the oven. Brush with egg wash and bake on 200 c or 370 f for 12-15 min. Take out brush with butter and dip in sugar cardamom. Serve and devour!
