Generously butter a deep 9-½-inch pie plate. Place 1 phyllo sheet on your work surface (cover remaining pieces with damp towel or plastic wrap). Brush the sheet lightly with butter and fold in half lengthwise. Brush folded surface with butter. Cut in half crosswise. Place 1 phyllo rectangle buttered side down in pie plate, covering bottom and letting it overhang the edge by ½ inch. Brush top of phyllo dough in pie plate with butter. Place second phyllo rectangle crosswise in pie plate, covering bottom and letting it overhang the remainder of the pie plate by ½ inch; brush with butter. Repeat process with remaining 4 phyllo sheets. Fold overhanging pastry under to form crust edge flush with edge of pie plate. Brush with butter. (Can be prepared a day ahead, if covered and refrigerated.)
Preheat oven to 350 degrees F. Whisk egg yolks and mustard in medium bowl to blend; beat in eggs, half-and-half, cream, salmon, scallions, and dill. Salt and pepper to taste (remember that the salmon is quite salty). Pour mixture into prepared crust and bake until center is set, about 50 minutes. Transfer to rack and cool. Garnish and serve at room temperature or slightly warm.