Add the sugar and salt to a large bowl and whisk everything together.
Melt the butter (either in a saucepan or in the microwave) and pour it into the bowl with the sugar and salt. Whisk it well to combine.
Lightly beat the eggs and the vanilla together and add it to the sugar mixture. Whisk everything until the mixture is smooth.
Add the Biscoff spread and mix it again with the whisk to combine everything. There's no need to melt the Biscoff spread.
In another bowl, stir together the flour and the baking powder.
Gradually add a little flour to the sugar/egg mixture while whisking continuously. I like to do this in 2 batches. Whisk the mixture until it's creamy and there are no lumps.
Add the chopped white chocolate and half of the cookies, broken into pieces. I like breaking them by hand. Then fold everything together with a rubber spatula.
Transfer the batter to the prepared pan and spread it evenly to all corners using the spatula. Make sure to even the surface, too.
Top the batter with the remaining cookies, either whole or broken in half.
Bake for 30-35 minutes, or until a toothpick inserted in the middle comes out with a few crumbs. (For a softer center, bake for 25-30 minutes.)
When done, remove the blondies from the oven and leave them in the pan for about 30 minutes.
Then use the edges of the overhanging parchment paper to lift them out of the pan onto a wire rack to cool completely.
Cut into squares and drizzle with some melted Biscoff spread.