1. Season the salmon steaks with salt and pepper.
2. Preheat the oven to 120°C (250°F) Gas 2.
3. Cut the lime rind into julienne strips. Blanch strips in boiling water for 1 minute. Drain well.
4. Heat 2 tbsp of butter in a large frying pan. Add the salmon and saute over a medium-high heat until lightly browned, about 4 minutes per side.
5. Transfer the salmon to a plate, cover, and keep warm in oven.
6. Add the lime juice, lime rind and walnut oil to pan. Stir well and cook over a low heat until the mixture is just heated through.
7. Whisk in the remaining butter 1 tbsp at a time.
8. Be careful not to let the sauce get too hot.
9. Remove the pan from the heat and let it cool slightly if necessary. The sauce should be slightly thick, the same consistency as Hollandaise sauce.
10. Season with salt and pepper and remove from heat.
11. Remove the salmon from oven. Spoon sauce over steaks and serve.