In the bowl of a stand mixer fitted with the paddle attachment, add the butter and sugars and cream together until smooth. Add the apples and mix well to combine.
In a large bowl, sift together the flour, oats, baking soda and salt. With the stand mixer running on its lowest speed, add the flour mixture a little at a time until fully incorporated.
Add the hot water to the stand mixer and mix on low until smooth.
Use a medium cookie scoop, or two tablespoons, to drop the cookie dough in mounds on a parchment-lined baking sheet.
Bake for 8-10 minutes until golden.
Transfer cookies to a cooking rack and let cool completely.
To make the glaze: Stir together the glaze ingredients. Drizzle on completely cooled cookies and let sit for at least 30 minutes to set. For easy cleanup, set the cooling rack on top of a parchment lined baking sheet before glazing.
Recipe by Maine Course at https://mainecourse.bdnblogs.com/2015/09/22/recipes/iced-apple-oatmeal-cookies/