Line an 8" x 8" baking dish with parchment paper. Leave some overhang to use as handles to lift the fudge out when it's ready.

Put a large pot over medium heat and melt the butter.

When it's all melted, add the peanut butter and cookie butter. Stir until fully dissolved and incorporated.

Add the vanilla extract and cardamom and stir.

Add the powdered sugar and stir until well incorporated. It should be a big semi hard ball. Just, work it until it's well mixed and most of the large white spots are gone.

Put the fudge into the baking dish and smooth it out with a silicone spatula. Refrigerate for 2 hours.

When the fudge has set, grab the parchment paper handles. Lift it out and transfer to a cutting board. Cut into inch and a half squares.