Soft, chewy cookies meet fluffy, homemade marshmallow filling in these oatmeal cream pies! This recipe makes 20 sandwich cookies in under 2 hours. Don't forget to watch the how-to video!
Gradually stir dry ingredients into butter mixture until thoroughly combined.
Stir in oats until well-distributed.
2 cups instant/quick oats
Drop batter by level 1 ½-Tablespoon-sized scoop onto prepared baking sheet and bake on 350F (175C) for 10 minutes or until edges are beginning to turn golden brown. Allow cookies to cool completely on baking sheet before filling.
For Marshmallow Cream Filling (see note for alternative filling options)
Before you begin: You will need a double boiler for this recipe. I recommend using the metal bowl of a stand mixer and a saucepan that is large enough to support the bowl without it touching the bottom of the pan. While this recipe can be prepped with an electric hand mixer, please note that it will be quite an arm workout and will take a long time and I recommend using a stand mixer if you have one).
In the completely clean, dry and grease-free bowl of a stand mixer, combine egg whites, sugar, cream of tartar and salt and whisk to combine.
6 large egg whites, 1 ½ cups granulated sugar, ½ teaspoon cream of tartar, ¼ teaspoon salt
Bring 1 ½-2” (4-5cm) of water to a simmer over medium-low in a medium-sized saucepan (use a saucepan that your mixing bowl will fit in without touching the bottom of the pan).
Place mixing bowl over simmering water and whisk constantly until the sugar is dissolved (if you rub a small bit of the syrup between your fingers (be careful, it’s hot!) it should no longer feel gritty at all) and the mixture reaches at least 160F (70C).
Remove mixing bowl from heat and fit it into your mixer. Using a whisk attachment, beat the egg whites on medium-high speed until mixture becomes thick and glossy and you have billowy stiff peaks. This typically takes approximately 5-10 minutes with a stand mixer but will take longer if you are using a hand mixer with beaters.
Stir in vanilla extract.
1 ½ teaspoons vanilla extract
Assembly
Once cookies have cooled, scoop a generous portion (I use about 2 Tablespoons) of marshmallow cream filling onto the bottom of one cookie. Top with another cookie to make a sandwich/marshmallow cream pie. Serve and enjoy!
Video
Notes
Other filling options
The marshmallow cream in this recipe is the closest to authentic oatmeal cream pies and is what I recommend for best taste. However, if you’re looking for something faster/simpler you can use one of my other frosting recipes instead, such as my cream cheese frosting, classic buttercream frosting, ermine frosting, etc.
Storing
Store assembled cookies at room temperature in an airtight container for up to 3 days.
Making in advance
The cookies may be prepared up to 3 days in advance of assembly.I personally prefer to use the marshmallow cream immediately but it may be prepared up to 24 hours in advance. To store, place in an airtight container and refrigerate. You will need to let it sit at room temperature and then most likely re-whip with a whisk attachment for several minutes to restore to original fluffy consistency before using. Note that the cream does not need to be refrigerated once the cookies are assembled, but doing so extends its life which is why I recommend refrigerating when making in advance.