Mix together 2 tablespoons each olive oil, sweet mustard, and dill. Brush the mixture on the salmon fillets; season with salt and pepper. Preheat oven to 350 degrees F, brush a baking sheet with some melted butter. Unroll the phyllo dough and lay a sheet flat on a work surface. Brush the sheet with melted butter, then dust with some caraway and dill. Repeat with 2 more sheets of phyllo, stacking on top of each other. With a sharp knife or pizza cutter, remove 4-inches off the side of the sheets to form a square. Now, cut criss-cross to make 4 even squares. Transfer the squares to the baking sheet. Lay a piece of salmon in the center of each square and fold up the corners. As you work, keep the phyllo covered with a damp, not wet, towel to prevent drying out. Brush the pastry lightly with butter and bake for 25 minutes or until the fish is opaque. In the meantime prepare the potatoes.
Coat a saute pan with olive oil and cook the leeks until translucent. Cut the roasted potatoes in half lengthwise and place face down in the pan to give them color. Add creme fraiche, remaining mustard, dill, and currants. Cook over low heat until heated through, about 5 minutes.
To serve: divide the potato mixture among 4 shallow bowls, mound a handful of greens on top followed by the salmon phyllo. Garnish with salmon caviar and serve immediately.