In a large bowl, put the butter and the sugar and beat, using a hand held mixer, until it is soft and fluffy (should take about 3 to 4 minutes). Beat in the eggs, one at a time and then the vanilla extract.
Sift together the flour, baking powder and salt and add it to the bigger bowl. Beat on slow speed until the flour has just mixed in. If the dough seems a little soft and sticky, refrigerate it for about half an hour so that it becomes easier to handle.
Divide the dough into three equal portions. Leave one portion plain. Add enough orange food colour to the second portion and green food colour to the third portion to get the shade you want. Knead the colour in so there are no streaks and the colour is uniform. If youu2019re using liquid colour you might need to add about a tbsp. of flour to each portion (not more) while kneading. Shape each portion into a ball, wrap in cling film and refrigerate for about an hour till firm again.
Now take each portion and roll it out, using your palms, into a thick log that is about 1 1/2" in diameter. All the three logs should be more or less of the same length. If theyu2019re not, you can trim the lengths to make them equal later. Refrigerate again, if necessary.
Now, using a rolling pin, gently flatten each log lengthwise until it is about 2u201d to 2 1/2" in width and about 1u201d to 1 1/4" in height.
Stack the uncoloured portion on the green coloured dough and the orange coloured dough over this. Gently press/ roll along the length of the stack so that the three layers stick together without flattening it out any more. If you donu2019t the layers will separate out when the cookies bake. Also make sure your layers are even and the same thickness or your finished cookie will have uneven layers!
You can cut the stack into two halves (along the length) to make it easy to store in the fridge. Wrap the cookie dough stacks in cling film and refrigerate for at least 6 to 8 hours or upto 3 days. You can also freeze them if want to store it for longer. If you freeze them, you can let them u201cthawu201d in the fridge overnight before slicing them.
When youu2019re ready to bake the cookies, take the stacks out and slice them with a sharp knife into 1/4" slices. Place the slices on ungreased cookie sheets or sheets lined with parchment. Leave about 2u201d between cookies as they will spread out during baking. Return the cookie sheets to the fridge for half an hour. This will ensure that they do not spread too much.
Bake them at 180C (350F) for 10 to 12 minutes till theyu2019re pale golden. Do not let them brown. Let the cookies cool on the sheets for about 5 minutes, then carefully lift them off and cool completely on racks.
Once they are cool, pipe a small wheel with spokes in the centre using blue coloured Royal Icing. Let the icing dry completely, then stack the cookies in an airtight tin.