Sieve together flour and salt. Shape a well and pour in hot water and oil. Mix the dough and knead for 2 to 3 minutes until it becomes soft and smooth. Add more flour if necessary. Wrap the dough in plastic wrap and let it rest on the countertop for 30 to 60 minutes.
Cut the dough into 2 pieces. On a floured work surface, roll out the dough to 1 mm (1/16 inch) thickness. Cut out 12 circles of 8 cm (3 1/4 inches) with a die-cutter.
In a pan, cook meat and leek over medium-high heat until meat loses its pink colour. Degrease and let it cool.
In a bowl, mix the mashed potatoes, meat, cheese and sour cream. Adjust seasoning and set aside.
Place about 20 ml (4 teaspoons) of stuffing on the circles. Moisten the edges and close in a half-moon shape, pinching the edges well.
Cook pierogi in salted boiling water for about 2 minutes. Drain and place pierogi on a lightly oiled plate.
In a pan, brown the pierogi in butter over medium-high heat for 1 to 2 minutes.
Serve with sour cream and sprinkle with chives and caraway.