To make the curing mix: place the salt, sugar and white pepper into a medium sized bowl. Add the dill and stir to combine.
Line a large, shallow, rectangular dish, to fit the salmon, with plastic wrap. Sprinkle over a quarter of the curing mixture, spread over the base and top with one of the salmon fillets, skin-side down.
Sprinkle over half of the cure and top with the other half of the salmon skin-side up.
Sprinkle over the remaining curing mixture on top of the fillet and wrap up in the plastic wrap.
Weigh the fish down with some cans or weights on top to remove any excess liquid or moisture.
Place in fridge, turning the salmon over every 6 hours, for 3-4 days, where possible.
Before serving the gravlax, rinse the cure off the fish to remove the salt and pat dry with kitchen paper.
Sprinkle the remaining dill over one side of the salmon and then sandwich the two fillets together again.
Wrap tightly in plastic wrap and chill for 6 hours.
To make the sauce: in a large bowl whisk the mustard and sugar together with the egg yolk.
Gradually whisk in a steady trickle of oil, making sure the oil is well emulsified. Start to add the oil at a constant pace.
Add the fresh dill and mix well.
To serve, cut the gravlax thinly (gravlax is traditionally served thicker than smoked salmon).
Place 3-4 good slices on a plate along with a spoonful of the sauce.