Make the Hollandaise:
Add egg yolks, lemon juice, salt, and cayenne to a blender. Blend for 20 seconds.
While blending, slowly stream in the hot melted butter until the sauce thickens and turns glossy. Set aside.
Poach the Eggs:
Fill a saucepan with 2-3 inches of water and bring to a gentle simmer. Add white vinegar.
Crack each egg into a small bowl. Swirl the water to create a vortex and gently slide the egg into the center.
Cook for 3-4 minutes until whites are set and yolk is runny. Remove with a slotted spoon and drain on paper towels.
Assemble:
Toast the bread until golden and crispy.
Mash the avocado with lemon juice, salt, and pepper. Spread generously on each toast.
Layer 2-3 slices of smoked salmon over the avocado.
Top with a poached egg, centered in the middle.
Spoon warm hollandaise sauce over the egg.
Garnish with fresh dill or chives. Serve immediately.