In the bowl of a mixer or in a large bowl with a hand mixer, cream butter and brown sugar on medium speed until light and fluffy, 3-4 minutes.
Add vanilla and salt and blend until combined.
With mixer on low, slowly add flour and cocoa powder to bowl until well combined. Mixture will likely look crumbly.
Keep mixer on low and add milk in until dough comes together. Mix in red food coloring and mini chocolate chips until just combined.
Remove pan with cookie crust from freezer and press cookie dough into an even layer over cookie crust.
Pour white chocolate ganache over the top of the dough and smooth evenly with a spatula. Sprinkle sprinkles over ganache.
Place pan in fridge chill for at least 45 minutes. Once chilled, remove bars from pan by lifting foil. Using a sharp knife, slice into squares.