Clean and wash broccoli and cut into florets. Peel and chop stems. Bring the water to the boil, stir the stock into the boiling water, add the broccoli and cook covered for about 5 minutes. Lift out and save the broth.
Peel and dice the onion, sauté in the hot fat, dust over the flour and sweat while stirring. Deglaze with the stock and cream, bring to the boil and simmer for 4-5 minutes.
Cut the smoked salmon into fine strips and add to the sauce. Add the broccoli again, heat briefly. Season to taste with salt, pepper and lemon juice.