In a small saucepan over low heat, melt butter.
Add garlic and cook for 30 seconds until fragrant.
Stir in saffron threads and let them bloom for 1 minute.
Add heavy cream, lemon juice, lemon zest, and Dijon mustard.
Simmer on low heat for 3-4 minutes, stirring occasionally, until the sauce thickens.
Season with salt & pepper to taste. Keep warm while preparing the salmon.