Arrange all ingredients for use.
Crumble the yeast into a small bowl and stir in the sugar and a little milk until smooth. Melt the butter.
Sieve the flour into a bowl. Add the dissolved yeast, 1 tsp salt and the remaining milk and mix. Add 2-3 tbsp butter.
Knead to a smooth dough, adding extra milk or flour if needed. Cover and leave to rise for about 30 minutes.
Wash the spinach and shake dry. Finely dice the feta.
Place 2 tbsp butter in a hot pan, crush in the garlic, add the spinach and allow to wilt. Season with a little salt and nutmeg, remove from the heat and add the feta.
Preheat the oven to 180°C (160°C fan, gas 4). Line a baking tray with baking paper.
On a floured surface, roll out the dough to about 3-4mm thickness.
Cut out circles, 8-10 cm in diameter.
Place 1-2 tbsp of the filling in the centre of each circle. Fold over the pastry to enclose the filling. Press the edges well to seal and pinch with fingertips.
Place on the baking tray and brush with beaten egg yolk. Bake in the oven for 25-30 minutes until golden brown.