Onion, Apple and Gruyere Tart

Pastry:
In large bowl, whisk together flour, salt and dry mustard. Using pastry blender or 2 knives, cut in butter until in coarse crumbs. In liquid measure and using fork, beat egg yolk with vinegar until frothy; pour in enough ice water to make 1/3 cup (75 mL). Drizzle over flour mixture, stirring briskly with fork unitl dough holds together. Press into ball; flatten into disc. Wrap in plastic wrap and refrigerate for 30 minutes. Make-ahead: Refrigerate for up to 3 days; let stand at room temperature for 15 minutes before rolling out.)

On lightly floured surface, roll out pastry into 12-inch (30 cm) circle; fit over bottom and all the way up side of 8-inch (2 L) springform pan. Refrigerate until firm, about 30 minutes. Line pastry with foil; fill evenly with pie weights or dried beans. Bake in bottom third of 400ºF (200ºC) oven until firm, about 20 minutes. Remove weights and foil; bake until light golden, about 10 minutes. Let cool on rack.

Meanwhile, in skillet, melt butter over medium heat; cook onion, stirring often, until softened, about 5 minutes. Increase heat to medium-high; add apples and saute or 2 minutes. Set aside.

In bowl, whisk together eggs, cream, parsley, chives, rosemary, mustard, salt and pepper. Sprinkle half of the cheese evenly over prepared crust. Spread apple mixture over top. Slowly pour egg mixture over top; sprinkle with remaining cheese.

Bake in bottom thrid of 375ºF (190ºC) oven until golden and knife inserted in centre comes out clean, about 30 minutes.

Source : Canadian Living Magazine: July 2004