Place a piece of grease proof paper into an 8x8 inch square pan and leave to one side.
Place butter, flours, sugar, salt and vanilla into a large bowl, or the bowl of your stand mixer and beat on medium-high speed until you have a crumbly mixture which is just starting to come together. The butter will be pea sized, although some larger lumps are fine.
Add in the Funfetti and 1tbsp of milk, then mix until well combined. Add in another 1tbsp of milk and then mix until a soft dough forms.
Tip the dough into your lined pan and press into a level layer. Use your hands or the base of a glass/cup.
Place in the fridge for 10-15 minutes. Whilst chilling, preheat the oven to 160C/325F and line 2 baking trays.
Once chilled, lift out the dough from the square pan and place on a cutting board. Either with a knife, or pizza cutter (I used a pizza cutter), slice into bite size pieces. My pieces were around 1/2 an inch-3/4 inch thick. I made around 64 bites. You can make them however big or small you want.
Separate all the shortbread bites and then place them onto your lined trays, leaving a little gap between each one.
Place in the oven for 12-17 minutes (depending on how big they are) until they look matte when the light from the oven hits them. If they look a little dark/soggy in the light, they're are not done.
You don't want them to be golden or coloured in anyway, just slightly firm to the touch and matte.
Leave to cool on the trays completely, before transferring to an airtight container. Funfetti Shortbread Bites will keep at room temperature for 5 days.