Making the Caramel -- Tip the sugar into a 10-inch-diameter non-stick skillet (or well-seasoned cast iron skillet). Set the skillet over medium-low heat. Meanwhile, put the cream and butter in a microwave-safe bowl or glass measure, and microwave on HIGH just until the butter melts -- about 1 minute.
While stirring with a metal spoon from time to time, let the sugar cook until it liquifies and turns a chestnut-brown color -- about 10 minutes. Off heat, slowly stir in the hot cream mixture. (Don't panic if the sugar crystalizes, or "seizes." Just bring the caramel to an exited boil while stirring it constantly, until most if not all of the hardened clumps dissolve.)
Straining the caramel and adding the cranberries and almonds -- Preheat the oven to 350°F. Pour the caramel through a wire mesh sieve set over a large bowl. Cool for 20 minutes. Add the cranberries and almonds, and stir until the berries and nuts are completely coated with caramel.
Filling and baking the tart -- Put the tart shell (in its pan) on a baking sheet. Fill the shell with the cranberry mixture. Bake until the caramel begins to bubble along the sides of the tart -- 25-30 minutes.
Cooling, unmolding, and serving the tart -- Let the tart cool to room temperature on a wire rack, then transfer to the refrigerator for at least 1 hour. (Or, cover the tart and refrigerate for up to 2 days.) When ready to serve, unmold the tart onto a large plate or platter. Cut the tart into 8 wedges, and serve cold or at room temperature.