Preheat the oven to 180°C. Line a roasting dish with parchment paper.
Brush the skin of the salmon with oil, then place it on top of the parchment paper.
Using a pestle and mortar, crush the juniper berries, coriander seeds, peppercorns and salt. Then add the sugar and combine. Add the vodka/gin, lemon juice and dill and mix to make a rough paste.
Smear this mixture over the salmon and put the lemon slices on top. Bake for about 15-20 minutes, depending on the thickness of the salmon), until the salmon has just cooked through.
Remove the dish from the oven and let the salmon rest (covered) for 10 minutes.
Meanwhile, make the sauce. Mix the two mustards, sugar and vinegar in a bowl, then whisk in the oil until emulsified. Add the dill and season to taste. You could add a squeeze of lemon juice too.
Carefully transfer the salmon onto a platter and serve with the mustard sauce.