Oatmeal Cookies

Preheat the oven to 350F (180C or 170C fan-forced). Line cookie sheets with silicone baking mats or baking paper.
In a large bowl, beat together the butter, brown sugar, and granulated sugar until fluffy.
Mix in the molasses, vanilla extract, and eggs until creamy.
Turn off the mixer and add in the flour, cinnamon, baking soda, and salt. Do a few stirs by hand first, then turn the mixer to a low speed and beat until incorporated.
Stir in the oats.
Form the cookies into balls about 1 to 1.5 tablespoons in size and place 2 inches apart on the lined cookie sheets. Use a cookie scoop for this. You should get about 32-34 cookies, making 16-17 sandwiches.
Bake 1 sheet of cookies at a time in the middle of the preheated oven for about 9-11 minutes, or until the tops look set.
Cool on the cookie sheet for at least 10 minutes before transferring to a wire rack to continue cooling.
Frosting

In a large bowl, beat the butter until fluffy.
Chop the cream cheese into 3-4 pieces, then beat into the butter.
Add in 1 1/2 cups powdered sugar, vanilla, and salt. Start with the mixer on a low speed, then gradually increase to a medium speed until the ingredients are incorporated.
Beat in the rest of the powdered sugar about 1/2 cup at a time until the desired sweetness is reached. If needed, beat in 1 tablespoon of cream if the frosting is too thick.
Assembling the Cookies

Take 1 cooled cookie and frost the bottom with about 1 to 1.5 tablespoons of frosting.
Sandwich a second cookie on top with the bottom facing down.