Separate the yolks of the salted duck eggs. Mash the yolks. Set aside.
In a sauce pan over medium heat, add oil and melt butter. Add mashed salted egg yolks. Mix well with a whisk. Add bay leaves. Season with salt, pepper, and chili flakes. Set aside.
Cook fries. Drain and transfer to a mixing bowl.
Add salted egg yolk sauce to the fries (heat before adding if clumped or hardened). Toss until well incorporated.