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.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.