Whisk flour and baking soda together in a medium bowl and set aside.
Melt 14 tablespoons butter in a saucepan over medium heat until melted (could also be down in a bowl in the microwave- just be careful and cover the bowl so the butter doesn't splatter).
Transfer melted butter to a mixing bowl. Add brown sugar, granulated sugar, salt, and vanilla to the mixing bowl. Whisk until incorporated. Add the egg and egg yolk; whisk until the mixture is smooth with no sugar lumps remaining, about 30 seconds. Let mixture stand for 3 minutes, then whisk for 30 seconds. Repeat until the mixture is thick, smooth, and shiny.
Using rubber spatula, stir in flour mixture just until incorporated (about 1 minute). Stir in sprinkles and chocolate chips. Give dough one final stir to ensure all flour is incorporated.
Chill dough for 1-2 hours.
When ready, preheat oven to 375 degrees. Grease a muffin tin with non-stick spray or line with muffin/cupcake liners. Scoop 1 tablespoon of dough and press into the bottom of a cupcake well covering the bottom. Top with an Oreo cookie. Scoop a second tablespoon of dough and press on top, being sure to cover up the Oreo. Repeat with the remaining dough and cookies.
Bake for 12-15 minutes until the cookies are golden brown and still puffy and edges have begun to set. Transfer cupcake pan to a wire rack; allow cookies to cool before removing from the cupcake pan. If the edges are slightly stuck, carefully run a knife along the edge to loose. Place the cookie cupcakes on a wire rack to fully cool before adding the frosting on top.
To make the frosting: In a clean and dry stand mixer bowl with paddle attachment, add the butter and cream until smooth and fluffy about 3 minutes. Add in the powdered sugar 1/2 cup at a time, full incorporating before adding more. Once all the powdered sugar has been added, stop mixer and add in the heavy cream and vanilla extract. Start the mixer slowly and after about 1 minute increase speed to medium and mix for 8 minutes until light and fluffy.
To assemble the cupcakes: Using the Ateco tip and piping bag, fill with the vanilla buttercream and swirl the frosting on top of each cupcake. If desired, add more sprinkles on top!
Can be stored in the refrigerator for up to 2 days- allow to come to room temperature again before serving due to the high amount of butter in the frosting. You could freeze the cookie cupcakes as well. Freeze before adding the frosting in a airtight container or zip-loc bag. Add frosting once cookies have defrosted.