Preheat your oven at 180C/gas mark 4.
Place the flour along with the thyme in a bowl and mix.
Add the cold butter in the bowl and mix with the tip of your fingers until it resembles fine breadcrumbs.
Add the cheese, grated and keep mixing by hand.
Finally add in the egg yolk (keep the white for brushing) and use a fork to mix it in.
Use your hand to form the dough until it no longer stick to the side of the bowl.
Place the dough on a surface lightly dusted with flour and roll it out at about 0.5 cm. Use a cookie cutter to shape and transfer on a lined baking tray, spacing them apart. For the leftover dough, simply reshape, roll out again and cut in the shapes you like until you use it all up.
Before baking, brush the tops with the egg wash ( egg white from 1 egg plus 1 tablespoon of water)
Sprinkle with nigella seeds or other seeds of your liking.
They will be ready in 20 minutes, when the tops get a golden colour.
You can keep them in an air-tight container up to 3 days.