First up, preheat the oven to 180 degrees celsius. Then, line the base and size of a 20cm square pan with baking paper. To make the cake, put milk and butter in a small saucepan over medium heat.
Keep stirring for about 2 minutes or until the butter is golden brown. Set aside to cool slightly. Add brown sugar, caster sugar, apple sauce, an egg and whisk to combine.
Place flour, bi-carb soda, cinnamon and salt in a large bowl. Add the apple sauce mixture and stir until just combined. Spoon the cake mixture into the pan and smooth the surface. Pop the cake in the oven and bake for 30 to 35 minutes.
To test that the cake is cooked insert a skewer into the centre of the cake. It should come out clean. Cool the cake in the pan for about 10 minutes, then use the paper to lift it out onto a wire rack to cool completely.
For the brown butter icing, melt more butter in a small saucepan over medium heat stir for 3 minutes or until the butter is golden brown. Pour into a heatproof bowl and pop in the fridge for 1 hour. When the butter is firm, beat it with an electric mixer until it's very pale. Gradually add icing sugar, beating well after each addition. Keep beating for about 4 minutes or until the icing is pale and fluffy place the cake on a serving plate and spread the brown butter icing over the top.
Then, cut it into pieces and drizzle with caramel sauce. This beautiful spiced apple cake with brown butter icing is easy to whip up using basic ingredients from your fridge and pantry.