Preheat the oven to 350°F. Butter and flour an 8×8 inch square baking dish.
In a large bowl combine the flour, baking powder, and salt.
In a medium bowl melt the butter in the microwave, 30 seconds at a time. Add the brown sugar and stir to combine.
In a separate small bowl add the Biscoff Cookie Butter and microwave, 30 seconds at a time until melted. Add ¼ cup only of the melted Biscoff to the butter/sugar mixture. The remaining half will be used to drizzle on top of the blondie batter before baking.
Add the vanilla extract. Test to make sure the ingredients are not too warm (should be room temperature), then add the egg and combine.
Add the wet ingredients to the dry ingredients and stir gently to combine. Do not overmix.
Press the batter into the baking dish. Drizzle with the remaining ¼ cup Biscoff.
Bake at 350°F for 25 minutes. Allow to cool before cutting and serving.
Notes
Biscoff Cookie Butter: This can be found in most grocery stores near the peanut butter section. Store-brand versions work well too.Dish Type: You can use a metal, ceramic, or glass dish as long as it is 8x8. There will not be enough batter to fill a 9x9 pan. Metal dishes take less time to bake in the oven, so if you using a metal dish, be sure to check it a few minutes early.Prevent Overmixing: Combining the wet and dry ingredients separately helps to prevent overmixing which leads to a tougher texture and consistency. I typically don't do this for many baked goods recipes, but I find that it makes a big difference for blondies.Using a spoon rather than a hand-held mixer may also help to prevent overmixing.