Peel and finely chop the onion. Heat 1 tbsp. oil in a pot, sauté onion in it, caramelise with sugar and deglaze with vinegar, add tomatoes and simmer for about 8 minutes. Season with salt and sugar.
Pass the tomato mixture through a sieve and let it cool down.
Clean, peel and cut the turnip and carrots into thick sticks. Spread them separately on a baking tray lined with baking paper. Sprinkle with 1 tsp. salt and paprika. Sprinkle with 2 tablespoons of oil and mix briefly on each baking tray.
Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 30 minutes. Take the vegetable fries out of the oven and arrange with ketchup.