The answer to yesterdays rhetorical question is "Not very long", evidently.
Note: I am aware that a rhetorical question is a question that doesn't require an answer, but I thought I'd head you off at the pass.
For the Bars:
1 cup firmly packed light brown sugar
2 teaspoons vanilla extract
1 teaspoon ground cinnamon
1/3 cup cookie butter (I used Lotus Speculoos Butter)
115g cake flour, sifted
For the Crumbled Cookie Topping:
40g unsalted butter, melted
1/2 cup crumbled cookies (I used Lotus Caramelised Biscuits)
1/4 cup firmly packed light brown sugar
2 tablespoons cake flour
2 teaspoons ground cinnamon
Make the Bars:
Preheat the oven to 180 degrees C. Spray a 20cm x 20cx cake pan with cooking oil spray and line with baking paper.
Put the cooled brown butter and the egg into a large bowl and whisk to combine. Add the brown sugar, vanilla, cinnamon and cookie butter and whisk until smooth. Stir in the flour, don't over mix. Pour the batter into the prepared pan.
Make the Crumbled Cookie Topping:
Put all the topping ingredients into a bowl and mix until you have a mixture that resemble rubble. Sprinkle the topping evenly over the batter.
bake for 30035 minutes, until the centre is set and the edges are pulling away from the sides of the pan, a toothpick should come out mostly clean. Allow to cool in the pan for at least 30 minutes until removing from the pan and slicing.