Special equipment: 2-quart baking dish; old-fashioned hand-crank ice cream machine
Ice Cream: Heat the milk and cream until scalded then turn off the heat. In a bowl whisk together the yolks and sugar; then temper the yolks with the hot cream mixture. Return to the heat and cook carefully stirring constantly until thickened and is 180 degrees F. Immediately pour the custard through a fine strainer into a bowl in an ice bath. Chill. Whisk in the vanilla extract. Turn in a hand crank ice cream machine with ice and rock or kosher salt and keep frozen.
Make the Crisp: Preheat the oven to 400 degrees F.
In a bowl, stir together the flour, sugars, cinnamon, and nutmeg. Using a pastry blender or the paddle attachment of an electric mixer, mix in the butter to make a crumbly, sandy mixture.
Peel, core, and thickly slice the pears and put them in a deep, buttered 2-quart baking dish. (The pears should be at least 2 1/2 inches deep in the pan; add more if necessary.) Drizzle the apple juice concentrate over the fruit and sprinkle the topping over the pears. Bake for 30 minutes, until pears are tender and topping is lightly browned.