Prepare the french fries in the oven according to the instructions on the packet. Cut the sausages diagonally into slices. Clean and wash the leek and cut it diagonally into thin rings. Drain the corn.
Melt the butter in a saucepan. Stir in the flour and toast briefly. Pour in the broth and cream and simmer for about 8 minutes. Season the sauce with mustard and ketchup and season with salt and pepper. Stir in the leek and corn and heat.