Sugar pie, a Belgian treat!
Add the self-raising flour and diced cold butter to a blender. Season with a tiny pinch of salt and the caster sugar.
Pulse into a dry mixture. Then add the egg yolk and tepid milk.
Pulse again until the dough comes together nicely. It shouldn’t be sticky at all.
Then transfer the dough to a lightly floured surface and knead it for 3 minutes. Wrap it in a sheet of cling film and put it aside to rest for at least 30 minutes.