In large bowl, beat Crisco, brown sugar, granulated sugar, molasses, vanilla and eggs. Add flour, salt, baking soda, cocoa and cinnamon. Mix in the oats.
Drop by ONE tablespoon onto a parchment lined cookie sheet. Bake 7-8 minutes in a 350 degree oven, until just starting to brown around the edges. DON’T OVERCOOK!
After cookies have cooled, combine hot water with salt and mix until salt is dissolved. In large bowl, beat marshmallow fluff with Crisco, powdered sugar and vanilla. Beat on high until fluffy.
Add in salt water and mix until well combined. Spread filling on one cooled cookie and press second cookie on top.
Store in airtight container at room temperature for up to a week.
Notes
Do not over bake the chocolate oatmeal cookies! They'll look soft and doughy and barely browned at the edges so you might be tempted to leave them in the oven longer. Trust me on this--they cool to a perfect chewy texture.
How long do oatmeal cream pies keep? Store these in an airtight container at room temperature for up to a week.
Can you substitute butter for the margarine or Crisco? No. For the cookies, the margarine (or shortening) helps achieve the chewy texture. Butter will make the cookies thinner and crispier so they won't have that authentic oatmeal cream pie texture and flavor.
How much filling to usein cream pies: I put about an inch of the marshmallow fluff filling between the cookies. You can use more or less depending on your preferences, just make sure to make them even!
Have leftover filling? I had just enough filling to fill my whoopie pies. If you end up using less filling and having leftovers, don't throw it out! It's delicious spread on graham crackers and fruit slices, too. Or you can eat it with a spoon. . . I won't tell.