Add sugar to a saucepan and place over medium high heat. Stir the saucepan until the sugar dissolves. Cook to brown, caramel color. Add the walnuts and baking soda. Stir well, remove from the heat and spread over a plate, covered with baking paper. Let it cool. Once cooled blitz to get a nice powder.
Preheat the oven to 170 °C / 340°F. Rinse and dry one apple. Cut it on very small cubes. Add 40g / 1.4 oz of butter to a saucepan and let it melt. Add the apple cubes and cook for about 5 minutes on medium heat. Remove from the heat and let cool a bit.
In a small bowl combine 70g / 2.5 oz of melted butter with lemon juice and calvados, or any other brandy. In a separate small bowl combine the brown sugar, ground hazelnuts, pinch of salt, cinnamon powder, cloves powder, ginger powder and nutmeg powder. Add the melted butter mixture and cooked apple cubes. Stir well.
baking and serve
Rinse and dry your apples. Use a paring knife to cut out the core of the apples, creating a hole that’s about 5 cm / 2 inches wide. Be careful not to cut through the bottom of the apples. Place the apples in a baking dish. Stuff the hazelnut mixture into the apples, place in the oven and bake for about 15 - 25 minutes or until the apples are tender. Let cool slightly, then serve warm with vanilla ice cream and sprinkle of walnut crocant.