1. Combine butter and brown sugar in a mixer with a paddle. Blend until uniform colour. 
2. Add egg yolks and mix well. 
3. Add flour and mix until it comes away from the side of the bowl.
4. Divide into 4 parts.                                                          
5. Add a few drops yellow paste food colouring to one part and mix well to blend colour. Remove and set aside.
6. Repeat process for each of the colours.
7. To make piñata cookies you will need two sizes of the same shape cookie cutters.
8. Roll out dough to one quarter inch thick.
9. Punch out four large size shapes and set two aside. With the remaining two, punch out the smaller cutter in centre of the shape.
10. Transfer outline of punched out cookie on top of your set aside cookie (large). Rub with water to seal layers together. Repeat as necessary with remaining shapes.
11. Bake at 350 F for 10 minutes.
12. Take out of oven and cool completely before removing from pans. 
13. Take one half of piñata cookie and fill with small candy treats.
14. Pipe around edges with royal icing.
15. Add second piñata cookie on top. 
16. Let sit for 10 minutes to solidify. 
17. Smash open and enjoy!

To make rainbow colour cookies, roll each colour of dough into a strip about one inch thick. Line dough up beside each other and roll out to a quarter inch thick. Create piñata cookies or just plain cookies with fun shapes.