Cream butter, sugar, and brown sugar together.
Add vanilla and salt.
Add eggs one at a time; beat well.
In another bowl, stir together flour, oats, baking soda, and cream of tartar.
Gradually add to butter mixture, beating until well blended.
Stir in chopped candy bars. Refrigerate dough 30 minutes to 1 hour.
Preheat oven 350 degrees.
Using a small ice cream scoop, scoop out cookies onto a cookie sheet.
Bake 10 to 12 minutes for soft cookies, 14 to 15 minutes for crispy cookies.
Remove from oven and cool on cookie sheet 2 minutes, then remove to wire rack to cool.To stuff cookies, make one or both of the frosting recipes below. These recipes make enough frosting for one 9-inch 3 layer cake. You may want to half the recipe for these cookies.
Spread icing on the bottom of one cookie and top with the other. Squeeze together to even out frosting. Enjoy!!