Tomato Potato Galette

In bowl, stir together flour, salt and cayenne pepper. With pastry blender or 2 knives, cut in butter and shortening until mixture is in fine crumbs with a few larger pieces. Stirring with fork, pour in vinegar and enough of the water to make dough hold together. Press into disc; wrap in plastic wrap and refrigerate until chilled, at least 30 minutes.

Filling: In large saucepan of boiling salted water, cover and cook potatoes just until tender, about 20 minutes. Drain and let cool. Thinly slice crosswise; transfer to large bowl.

Meanwhile, cut tomatoes lengthwise into 1/2-inch (1 cm) thick slices; place on foil-lined rimmed baking sheet. Sprinkle with pinch each of the salt and pepper; broil, turning once, until slightly shrivelled and edges are blackened, about 10 minutes. Let cool.

Meanwhile, in skillet, heat oil over medium heat; cook onions, garlic, rosemary and remaining salt and pepper, stirring occasionally, until onions are golden, about 10 minutes. Add to potatoes along with Asiago cheese and all but 1 tbsp (15 mL) of the eggs; toss gently to combine.

On lightly floured surface, roll out pastry to 16-inch (40 cm) circle; place on pizza pan. Spread potato mixture over pastry, leaving 2-inch (5 cm) border uncovered. Arrange tomatoes on potato mixture; sprinkle with Parmesan cheese. Fold border over top, pleating to fit. Brush pastry with remaining egg.

Bake in bottom third of 400°F (200°C) oven until pastry is golden, 40 to 45 minutes. Let stand on rack for 10 minutes before cutting. (Make-ahead: Let cool. Cover and refrigerate for up to 6 hours. Rewarm before serving.)