Ingredients
Produce
- 1 teaspoon vanilla extract
Dairy
- 1 cup unsalted butter
- 1 large egg
- 1 egg yolk
Pantry / Dry Goods
- 1 cup dark brown sugar
- ½ cup granulated sugar
- 1½ cups all-purpose flour
- 1½ cups old-fashioned oats
- 1 teaspoon baking soda
- 1½ teaspoons cinnamon
- ½ teaspoon salt
Cream Filling
Dairy
- ½ cup unsalted butter, softened
- ½ cup marshmallow fluff
Pantry / Dry Goods
- 1½ cups powdered sugar
- 1 teaspoon vanilla extract
- Pinch of salt
Instructions
Start by browning the butter. Melt it in a saucepan over medium heat, stirring constantly until it turns deep golden brown and smells nutty. You’ll see little brown bits at the bottom—that’s flavor. Pull it off the heat and let it cool slightly.
In a bowl, whisk together the brown butter, dark brown sugar, and granulated sugar until glossy and smooth.
Add the egg, egg yolk, and vanilla. Mix until fully combined and slightly thickened.
In another bowl, combine flour, oats, baking soda, cinnamon, and salt.
Add the dry ingredients into the wet and mix just until combined. The dough will be thick and slightly sticky.
Press about two-thirds of the dough into a parchment-lined baking pan, spreading it evenly.
Bake at 350°F until just set and lightly golden, about 10–12 minutes. Remove and let it cool slightly.
While that cools, make the cream filling by beating together butter, marshmallow fluff, powdered sugar, vanilla, and a pinch of salt until light and fluffy.
Spread the cream filling evenly over the base.
Take the remaining dough and gently press pieces over the top. It won’t fully cover—and that’s exactly what you want.
Return to the oven and bake until golden and set, about 15–18 minutes.
Let cool completely before slicing so the layers set clean.

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