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1
Preheat the oven to 425 degrees F. Line 2 baking sheets with silicon mats or parchment paper and set aside.
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2
For the cookies: Beat the butter and sugar with a hand mixer until light and fluffy.
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3
Add the egg and vanilla until just incorporated.
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4
Scrape down the sides of the bowl.
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5
In a separate bowl, whisk together the flour, cocoa powder, baking soda, salt and baking powder.
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6
In a third bowl, combine the milk and sour cream.
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7
Add half of the milk mixture to butter mixture while mixing on low speed.
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8
Then add half of the flour mixture and mix until incorporated.
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9
Repeat the process.
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10
With a measured scoop, portion out the batter into small rounds on the prepared baking sheets, spaced at least an inch apart.
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11
You can make the cookies whatever size you like; I like mine a bit big so I use a 4-ounce ice cream scoop.
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12
Bake until the tops lightly spring back when touched, 8 to 10 minutes.
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13
Remove from the oven and allow to cool completely.
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14
For the filling: Add the sliced strawberries to a bowl and sprinkle with the granulated sugar and let sit for 15 minutes.
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15
Preheat the oven to a broil and set a rack 6 inches from the broiler.
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16
When the cookies are cooled, place them round-side down and then top half of them with sliced strawberries.
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17
Press 3 marshmallows together using the palm of your hand, until mostly flattened, and then place them on the other half of the cookies.
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18
Place the marshmallow-covered cookies back on the baking sheets and place under the broiler to let the marshmallows char and soften until lightly golden on top, 1 to 4 minutes.
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19
Keep an eye on them as they can burn quickly.
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20
For assembly: Top the strawberry side of the cookie with one of the marshmallow cookies, gently press together and then stand back and marvel at your creation.
