1 Crumble yeast in 200 ml (approximately 3/4 cup) lukewarm water and dissolve while stirring.
2 Combine yeast mixture with flour, 3 tablespoons canola oil and 1 teaspoon salt in a mixing bowl. Knead with the dough hook of a hand mixer until smooth, cover with a clean kitchen towel and let rise until the dough has doubled in size, about 1 hour.
3 Meanwhile, peel the potatoes, rinse, dice, place in a pot with enough salted water to cover potatoes and cook for about 20 minutes. After 20 minutes, drain and let cool slightly.
4 While the potatoes are cooking, halve leek lengthwise, rinse thoroughly under running water and cut into thin rings.
5 Heat 2 tablespoons of oil in a pan and cook the leeks over medium heat until the liquid completely evaporates, 8-10 minutes. Put leeks in a bowl and add the cooled potatoes.
6 Thoroughly mix quark, sour cream and eggs with a hand mixer. Fold mixture into leeks and potatoes in the bowl and season to taste with salt, pepper and caraway seeds.
7 Brush a baking sheet with the remaining oil. Put the dough on sheet and spread with floured hands to the edges of the sheet.
8 Distribute leek and potato mixture on top of dough. Sprinkle with pumpkin seeds and bake in a preheated oven at 175°C (fan 150°C, gas mark 2) (approximately 350°F/convection 300°F) on the middle rack for 30-35 minutes. Cut into pieces while still hot or lukewarm and serve.