Place egg yolks and lemon juice in a 2-cup liquid measuring cup; season with a pinch of salt and pepper. Using an immersion blender, blend, slowly drizzling in the canola oil; continue blending until thickened and well combined. Season with salt and pepper and transfer to a small bowl.
Whisk vinegar into egg yolk mixture and fold in parsley, cornichons, capers, dill, chives, and tarragon. Season with salt and pepper and refrigerate until ready to use.