Start by making the Buttermilk Syrup Glaze. Combine the brown sugar, butter and buttermilk in a sauce pan over medium heat.
Stir constantly until the mixture begins to boil.
Once the mixture starts to bubble, remove from heat and stir in the baking soda and vanilla. The baking soda will cause the syrup to foam and bubble up.
Whisk in the powdered sugar until smooth. Set aside and allow it to cool while you bake the cookies.
Preheat the oven to 350°.
To make the cookies, cream together the butter and sugar with a stand mixer.
Scrape the sides and add in the eggs, and vanilla extract. Mix until combined.
Add the flour, pancake mix and baking soda to the mixer and mix until the cookie dough comes together.
Scoop and roll the cookies- use a generous 1/3 cup of dough for each cookie. Roll the cookies into a ball and then flatten the ball into a circle that is about 1inch thick and arrange on a cookie sheet. Repeat with the remaining dough.
Bake at 350° for 12-15 minutes or until the cookies have spread slightly, the centers of the cookies puff up, no longer look wet and glossy in the center and the edges are starting to turn golden brown.
Allow the cookies to cool on the pan for 10 minutes.
While the cookies are cooling, make the buttercream topping by creaming the butter until smooth.
Add 1/2 cup of powdered sugar at a time, mixing until incorporated before adding more. Add a splash of milk as needed to bring the powdered sugar and butter together. Repeat until all of the powdered sugar has been added.
Add in the vanilla. We will want to keep this buttercream pretty thick. Add a little more milk to adjust the texture and thickness, if needed.
While to cookies are still warm, spoon a generous amount of the cooled buttermilk syrup glaze onto each cookie.
Use a small cookie scoop to scoop a dollop of buttercream on top of the buttermilk syrup glaze and serve warm.