Preheat the oven to 180°C/ 350°F/Gas mark 4. Grease a 23cm/9in square baking tin.
In a large mixing bowl, cream the butter, sugar, eggs and vanilla essence using an electric mixer.
Combine the flour, baking powder, cinnamon and salt, then add to the butter mixture. Mix until the flour is moistened. Fold in the apples and pecan nuts.
Spread the mixture in the baking tin, and bake in the oven for 45 minutes. Allow to cool in the tin on a wire rack, then cut into squares and dust with icing sugar.