- With the rack in the middle position, preheat the oven to 350°F (180°C). Butter and line an 8-inch (20 cm) square, straight-edge pan with parchment paper, letting it hang over two sides.
- In a bowl, combine the flour, oats, baking soda and salt. Set aside.
- In another bowl, cream the butter and brown sugar with an electric mixer. Add the egg yolk and beat until smooth. At low speed or with a wooden spoon, stir in the dry ingredients until the mixture is crumbly in texture.
- Press two-thirds of the mixture into the pan. Spread with the caramel sauce and sprinkle with 3 1/2 oz (100 g) of the chocolate. Cover with the remaining dough and chocolate (1 1/2 oz / 40 g).
- Bake for 25 minutes or until lightly golden brown. Let cool completely. Cut into squares.
- The squares will keep for 1 week in an airtight container at room temperature.