Line a baking tray with baking paper. Place flour, egg, oil and vinegar in a bowl; knead briefly to combine. Place on a lightly floured work surface and knead for 10 minutes; shape into a ball. Heat a ceramic bowl, invert it over dough. Leave dough to rest for 30 minutes.
For the filling, peel and chop the garlic. Heat oil in a large saucepan. Add all the vegetables and cook for 5 minutes. Add curry powder, lemon juice, egg yolk and cream; season with salt and pepper.
Preheat oven to 220 degrees C. Flatten pastry ball a little and cut into 12 equal pieces; stretch each piece into a rectangle approximately 8×30cm. Brush with oil.
Place 1 tbsp filling on a narrow end of a rectangle; fold over the opposite end and wrap pastry a few times diagonally around the filling to make a triangle. Make sure edges are sealed. Repeat with remaining pastry. Brush triangles generously with oil; place on baking tray. Bake for 20 minutes. Brush with beaten egg white and sprinkle with sesame seeds; bake for a further 5 minutes.