Line a 8 x 8 baking pan with wax or parchment paper. You can pray the paper with a little bit of oil to make sure it doesn't stick (optional)
Place the sugar into a food processor. Process for 30 seconds until the sugar is fine.
Combine sugar, milk, and butter in a medium sauce pan. Heat the pan to just melt the butter, then bring to a boil over medium high heat.
Boil for 5 minutes, do NOT stir during this time.
Remove from the heat. Stir in the white baking chips and food coloring. Keep mixing until it completely melts. It may look like it won't fully melt but just keep stirring.
Stir in the juice and zest.
Quickly place into your 8 x 8 pan. Smooth out with a spatula.
Allow to complete cool to set up before cutting.