Preheat the oven to 350F. Spray a 9x13-inch pan with nonstick spray. Make room in your freezer to put the pan after baking.
In a large bowl, use an electric mixer to combine the sugars with the butter and peanut butter. Add the egg, milk and vanilla and blend well.
Mix in the dry ingredients- flour, baking soda and salt.
Press the cookie dough evenly into the bottom of the prepared pan. Bake 19 to 24 minutes, until the cookie dough is set and baked through.
Press the kisses into the hot, baked cookie dough in 5 rows of 8. Place the pan in the freezer until the baked cookies are cold and the kisses are firm.
Remove the pan from the freezer and cut into 40 bars. Keep in a sealed container (or cover the pan with plastic wrap), and serve within a few days. You can freeze these in a sealed container too- for up to 3 months.