Preheat your oven to 325 degrees F. Prepare a 9”x13” metal baking dish by spraying the bottom and sides with nonstick spray. You can also want to line the bottom and side with parchment paper and spray again. Set aside. NOTE: you can use a glass baking dish but the bars will take a few minutes longer to bake and the edges might not be as crunchy.

In a medium size mixing bowl, whisk together the flour, baking soda, and salt. Set aside.

In the bowl of an electric mixer fitted with the paddle attachment, or with a hand beater, beat the butter and Biscoff cookie spread until smooth.

Add the brown sugar and granulated sugar and mix on medium-high speed for about a minute, making sure to scrape down the sides and bottom of the bowl as needed.

Add the eggs and beat until well mixed.

Stir in the flour mixture on low speed and mix until no streaks of flour remain.

Fold in the oats.

Put the batter into the prepared pan. It will be a thick batter, similar to cookie dough, but a little stickier. Evenly press the batter into the pan and bake for 20 minutes.

Remove the pan from the oven and allow to cool completely before adding the buttercream.

In the bowl of an electric mixer fitted with the paddle attachment, beat the butter and Biscoff cookie spread on medium-high speed until smooth.

With the mixer on low, gradually add the powdered sugar, followed by the vanilla. Turn the mixer to medium-high speed and beat until light and fluffy, about 2 to 3 minutes. Be sure to scrape down the sides and bottom of the bowl as needed.

Pipe or spread the buttercream on top of the room temperature bars.

You can also drizzle with melted white chocolate and Biscoff cookie crumbs.