For the Hollandaise:

1. Combine egg yolk, water, lemon juice, and a pinch of salt in the bottom of a cup that barely fits the head of an immersion blender.
2. Melt butter in a small saucepan over high heat, swirling constantly, until foaming subsides. Transfer butter to a 1 cup liquid measuring cup.
3. Place head of immersion blender into the bottom of the cup and turn it on. With the blender constantly running, slowly pour hot butter into cup. It should emulsify with the egg yolk and lemon juice. Continue pouring until all butter is added. Sauce should be thick and creamy. Combine the Hollandaise with two teaspoons dill and season to taste with salt and a pinch of cayenne pepper. Set aside and keep warm.

For the poached eggs:

1. Bring a medium pot of water to a simmer, then reduce heat until it is barely quivering (about 180°F/80°C on an instant-read thermometer).
2. Carefully break 1 egg into a small bowl, then tip into a fine mesh strainer. Carefully swirl egg around strainer, using your finger to rub off any excess loose egg whites that drop through. Gently tip egg into almost simmering water. Swirl gently with a wooden spoon for 10 seconds, just until egg begins to set.
3. Repeat straining and tipping with remaining eggs. Cook, swirling occasionally, until egg whites are fully set but yolks are still soft, about 4 minutes.
4. Carefully lift eggs from pot with a slotted spoon and place them onto a plate lined wih paper towel.

For assembling the toasts:

1. Mash the avocados, and season with salt, freshly ground pepper and a pinch of cayenne pepper.
2. Toast the English muffins and divide between 4 plates. Top each English muffin half with the avocado mash, 2 slices smoked salmon, then a poached egg. Spoon dill hollandaise sauce over each egg, garnish with extra dill and serve immediately.