Heat 1 tablespoon of rapeseed oil in a large pan over medium-high heat. Add the sausages and brown them for 2-3 minutes on all sides. Remove and set aside.
Peel the red onions and slice them into rings.
Reduce heat to medium. Heat the remaining 1 tablespoon of rapeseed oil in the same pan. Add the onion rings and sauté for 3-4 minutes until they soften.
Add both types of paprika powder and stir to coat the onions. Cook for 1 minute to bloom the spices.
Stir in the tomato paste and powdered sugar. Cook for 1 minute.
Dissolve the grain stock in 100 ml (about 1/2 cup) of water and pour into the pan, stirring well.
Return the sausages to the pan. Season with salt if needed. Reduce heat to medium-low and simmer for 15 minutes until the sausages are cooked through (internal temperature 63°C / 145°F).