- With the rack in the middle position, preheat the oven to 350°F (180°C). Butter an 8-inch (20 cm) square baking dish and line the bottom with a sheet of parchment paper, letting the paper hang over two sides.
- In a bowl, combine the flour and icing sugar. Add the butter and combine until the dough forms. Press onto the bottom of the prepared dish.
- Bake for 10 minutes or until light golden brown.
- Meanwhile, in a saucepan, bring the condensed milk and butter to a boil, then simmer for 5 minutes, whisking constantly. Pour the caramel over the warm shortbread.
- Bake for 15 minutes. Let cool completely on a wire rack.
- Place the chocolate and cream in a bowl. Microwave for 1 minute or until heated through. Using a spatula, stir until the chocolate is melted and the ganache is smooth. Spread over the cooled caramel. Immediately sprinkle with the pretzels. Let set for 1 hour at room temperature.
- Cut into squares. The millionaire shortbread with pretzels will keep for 1 week in an airtight container at room temperature.