In a stand mixer fitted with a paddle attachment, cream the butter.
Add the cookie butter and mix until fully combined.
With the mixer on low speed slowly add the powdered sugar. Once incorporated add the heavy cream and mix in.
Scrape down the sides and bottom and the bowl and then turn the mixer to high speed and beat for 4-5 minutes.
To decorate as we did, add a Wilton 1M tip to a piping bag and fill with buttercream. Swirl buttercream on each cupcake. If desired, drizzle with caramel sauce and top each cupcake with half a biscoff cookie. You can also melt some of the cookie butter and drizzle it on the cupcakes inplace of caramel sauce.