Wash the apples thoroughly and let them dry.
Use a special tool to core the apple (remove the seeds and leave a circular, vertical hole in each apple).
Then, fill this hole with a teaspoon of butter, walnuts, sugar, and cinnamon.
Top each apple off with a whole nut if desired and sprinkle with sugar.
Repeat the same process for each apple.
Place the fruits in a baking dish and add the water, cognac and cinnamon stick.
Bake the apples at 180ο C for 15-20 minutes, until well softened.
When the apples are ready, garnish with cinnamon and finely chopped walnuts, and serve immediately.
These baked apples are even more scrumptious served with vanilla ice cream, whipped cream or yogurt.