Almost all macarons use the same basic recipe for the two shells that hold whatever filling is chosen. We use the method presented here. Different colourings are used to give the finished product an appearance that best suits the chosen flavour. Here we used a green food colouring in attempt to reflect the apples in the filling.
You will find food colours easily in any supermarket. Many cookery writers insist that powdered colours are by far the best and these can be found easily from on-line patisserie suppliers. You will need to try out the various options available to find which suits you best. Colours are simply incorporated into the macaron mix along with the second part of egg white, mix the colour well into the egg white before adding it to the meringue so that it will blend easily into the final paste. Remember that colours change during cooking. Something that appears vivid in the raw paste will dull down considerably once baked.
These lemon macarons illustrate the change in colour after baking.
Ingredients
This recipe involves making a caramel, cooking apples and then combining the two to make a filling for macarons. The filling can be made well in advance of the macarons themselves. It stores well in the fridge for several days.
Apples 
Peel the apples and chop into small cubes
Melt the 25g butter in a heavy bottomed pan large enough for the apples.
Add the cubed apples and stir so that the pieces are coated with butter
Cover and leave the pan over a low heat for around ten minutes.
The apples should be starting to fall at the end of the cooking period, you will need to check and adjust your time according to the apples you have and the size of your cubes. Ideally they should form a rough purée but better to over cook than to find very hard pieces when you come to pipe the filling into the macarons.
Caramel
Place the sugar into a heavy bottomed pan and heat until it forms a caramel. Keep a close watch during this process, use a silicon spatula to stir the sugar around so that it melts evenly. Once all the grains are melted lower the heat and keep stirring until you have a light brown coloured caramel.
Keeping the heat very low add the 50g butter and stir until this has melted.
Add the cream (with caution, you are adding a water based ingredient to boiling sugar and the reaction can be dramatic).
Stir until all ingredients are mixed to a smooth caramel.
Allow both caramel and Apple to cool to room temperature.
Once the two components have cooled it is simply a matter of stirring the apple into the caramel so that you have a homogeneous mix. Transfer the resulting mixture to a disposable piping bag, snip off the end so that you have an opening of around 1cm and pipe generously onto your macaron shells.
If you have chosen to have larger pieces of apple rather than a smooth purée you might need to cut the piping bag a little higher so that the apple pieces can pass through.
Complete the macarons by adding a second shell to the top. Store in the refrigerator, remove 30 minutes before eating so that the macarons are near to room temperature.
The finished toffee apple mix can be stored either in a piping bag or a sealed container in the refrigerator for at least a week. Similarly the macarons can be stored for some days in the refrigerator, in fact they will improve if left 48 hours before eating.
This toffee apple paste can be used in numerous recipes in addition to macarons. We have used it to fill éclairs, as a base layer underneath fanned apples for an apple tart and as a centre for moulded chocolates. It would also be fine as a filling for sweet pancakes or with waffles. A really versatile way to put windfall apples to good use.