1.Combine flour, yeast, salt and sugar in large bowl. Make a well in the centre; using hand, mix in egg yolks, milk and butter until mixture is soft and elastic. Scrape down sides of bowl, cover; stand in warm place about 1 hour or until dough doubles in size.
2.Meanwhile, to make the filling, heat oil in large frying pan; cook onion, garlic, potato and bacon, stirring, until potato softens. Add beef; cook, stirring, until changed in colour. Stir in paste and thyme. Cool 10 minutes.
3.Turn dough onto floured surface; knead until smooth. Divide dough into 16 pieces; press each piece into 12cm round.
4.Preheat oven to 200°C. Lightly oil two oven trays.
5.Place rounded tablespoon of the filling in centre of each round; gather edges, pinch firmly to enclose filling. Place piroshki, pinched-side down, on prepared trays; brush with egg.
6.Stand, uncovered, in warm place 15 minutes. Bake, uncovered, in hot oven about 15 minutes or until golden brown.
For a lower-fat version, use no-fat milk and low-fat dairy-free spread instead of the butter. Piroshki are small Russian dumplings that can have various savoury or sweet fillings but this one is among the most traditional. Baked or fried, they make excellent hors d’oeuvres.