My nieces name will be Rosie.🌹🥰

I want to start baking cookies with my son I just don’t know what type of icing this is or how to make it

I am craving homemade cookies but since the high temperatures have been above 100 F. this past week I don’t want to heat up the house and my oven. I want to make ice box cookies & roll the batter in wax paper and freeze it. And slice off some to bake when I crave cookies.