- With the rack in the middle position, preheat the oven to 350°F (180°C). Butter an 8-inch (20 cm) square baking pan and line the bottom with a sheet of parchment paper, letting the paper hang over two sides.
- In a pot, bring the raisins, water, lemon juice and brown sugar to a boil. Add the baking soda and simmer for 5 minutes, stirring constantly until the raisins have broken down into a purée. Let cool.
- In a bowl, combine the oats, brown sugar, flour, almonds, pecans and baking powder. Add the butter and combine until the mixture sticks together. Press half of the crunch mixture over the bottom of the prepared pan. Spread the raisin mixture overtop. Sprinkle the remaining crunch on top and press down lightly.
- Bake for 40 minutes or until golden brown. Let cool completely.
- Cut into squares. The raisin nut squares will keep for 2 weeks in an airtight container at room temperature.