The frosting should be made in 2 stages. First, make the eggless cookie dough. Cream together the butter and brown sugar.
Add the milk and vanilla extract, mixing to combine. Slowly add the flour and salt, mixing on slow until just combined.
Mix in the mini chocolate chips if you'e going to use an extra-large open-star piping tip. If not, leave the chocolate chips out and instead use them as a garnish (they'll clog smaller piping tips, or any closed star tips). Set aside the eggless cookie dough.
For the frosting base, combine the butter and confectioners sugar, whipping until light and fluffy.
Add in the cookie dough to the frosting base and mix to fully combine.