Mix together the flour, yeast and 35g caster sugar and, either in a processor, with a freestanding mixer fitted with the flat paddle, or by hand as if you were making a crumble, mix the cold, cubed butter with the flour until you have a crumbly, sandy mixture with a few porridge-oats-sized pieces of butter.

Whisk or fork the egg yolks with the soured cream and add to the butter and flour mixture until you have a sticky dough. Divide it equally into quarters, shape each into a ball and then flatten to a patty. Wrap the patties and place them in the fridge for 1 hr (or for up to 2 days) to rest.

When you want to bake them, preheat the oven to 190ºC/170ºC fan/gas 5, get out a baking sheet and line it with baking paper. Take one of the patties of dough out of the fridge. Mix the 150g caster sugar and cinnamon together well, then halve. Sprinkle your first half over a clean, smooth surface, much in the way you’d normally sprinkle with flour when rolling out pastry.

Unwrap, and squidge the patty a bit in your fingers then flatten it a bit more. Place it in the centre of the cinnamon sugar, then flip it over and start rolling, turning it if it starts to stick, until you have a thin circle of about 28cm. Don’t worry if it isn’t a perfect circle! With a sharp knife, cut into quarters, and then cut each quarter into 4 so that you have 16 slender triangles. Starting from the wide end, roll up a triangle, and curl the ends a little, so that it looks like a tiny armadillo crossed with a mini croissant. Place it on the baking sheet and continue with the remaining 15. They don’t spread as they cook, so you don’t need to space them much apart.

Bake for 15 mins – they will still feel soft, but they crisp up on cooling – then transfer to a cooling rack. Take out the second ball of dough, proceed likewise. Use the remaining half of cinnamon sugar for the last 2 balls of dough.