Soft, chewy oatmeal cookies made with brown sugar and cinnamon are filled with fluffy homemade Italian meringue buttercream. These homemade oatmeal cream pies offer a rich, buttery filling that's less sweet than marshmallow cream and make a delicious treat to share with family and friends.
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In a large stand mixer, beat the butter and brown sugar until light and fluffy.
Add the eggs and vanilla. Beat again until smooth.
Add the flour, cinnamon, sea salt, and baking soda. Mix on low speed until just combined.
Add the oats and mix again on low speed until combined.
Cover and refrigerate the dough for one hour.
Preheat the oven to 350℉.
Line sheet pans with parchment paper.
Place 2 tbsp dough balls evenly on the sheet pans. (approx. 12 per pan)
Bake for 12-14 minutes or until edges and tops of the cookies are slightly browning.
Remove from the oven to a cooling rack. Allow the cookies to cool while preparing the cream filling.
In a stand mixer, using the whisk attachment, beat the egg whites and salt on high speed for 10 minutes.
While the egg whites are beating prepare the syrup by bringing the sugar and water to a simmer in a small saucepan.
Monitor the temperature of the syrup with a candy thermometer. It is ready to add to the egg whites when it reaches 240℉.
While the egg whites are beating and very fluffy, slowly pour the syrup down the side of the mixing bowl into the egg whites. Continue beating for 10 minutes.
Keep the mixer running and add the softened butter, 2 tbsp at a time.
Add the vanilla extract and beat until smooth and fluffy.
Spread cream filling onto the bottom side of 24 cookies and place the remaining cookies on top of each one. Can be served immediately, stored in an airtight container at room temperature, or wrapped and frozen.