1. Preheat the oven to 400°F (200°C). Line a baking tray with parchment paper.

2. In a small bowl, mix the softened butter with the egg and a pinch of salt until smooth.

3. Place the salmon fillet on the prepared tray and spread the butter mixture evenly over the top.

4. Bake the salmon for 12-15 minutes or until it flakes easily with a fork.

5. While the salmon is baking, prepare the lemon cream sauce. In a medium saucepan, heat the water with the vegetable bouillon cube and heavy cream. Bring to a boil, then reduce the heat and let it simmer for 5 minutes.

6. In a small bowl, mix the flour with the lemon zest until combined.

7. Gradually whisk the flour mixture into the simmering cream sauce, whisking constantly to prevent lumps.

8. Continue cooking the sauce for an additional 2-3 minutes until it thickens and becomes smooth.

9. Remove the saucepan from the heat and stir in the lemon juice, salt, and black pepper.

10. Carefully transfer the baked salmon to a serving platter and pour the warm lemon cream sauce over the top.

11. Garnish with fresh herbs if desired and serve immediately.