Whisk flour, sugar, lemon peel, and salt in medium bowl. Add butter; using fingertips, rub in butter until coarse meal forms. Drizzle 1/4 cup cream over; toss with fork until moist clumps form, adding more cream by teaspoonfuls as needed if dry. Gather dough into ball; flatten into disk. Wrap in plastic and chill 1 hour. DO AHEAD: Can be made 1 day ahead. Keep chilled. Let stand at room temperature 30 minutes before rolling out.
Preheat oven to 400°F. Mix all pears, sugar, flour, lemon juice, lemon peel, and nutmeg in large bowl to coat. Roll out pastry on sheet of floured parchment paper to 14-inch round. Transfer crust on parchment paper to baking sheet. Mound pears in center of pastry, leaving 2-inch plain border. Fold pastry border over pears, crimping slightly. Brush pastry edges with cream; sprinkle with sliced almonds.
Bake croustade until filling bubbles and almonds are lightly toasted, about 1 hour. Cool slightly. Serve croustade warm or at room temperature with vanilla ice cream, if desired.
