Cut your butter into slices. Add the sliced butter into a large mixing bowl (a stand mixer with a paddle attachment works great if you have it), and start to beat the butter, for about 1 minute.
Add the granulated sugar, and brown sugar, and beat for 2 minutes, until the batter is smooth and creamy.
Add in the eggs and vanilla extract, and stir until just combined.
Dump in the flour (I recommend doing the scoop and level method for measuring it out or you may end up with too much), cornstarch, baking soda, baking powder, and salt. Stir it together till you have a nice soft dough, scrape the bottom of the bowl as needed.
Divide your Biscoff cookies in half. Blend half of the cookies into a fine crumb using a blender or food processor. Chop the other half of the cookies up into small pieces (I like to reserve the pieces of 1 to 2 of the cookies, for topping the cookie dough balls - for best appearances).
Add the Biscoff cookie crumbs, pieces, and white chocolate chips (I also like to reserve 1/4 cup of the white chocolate chips for topping the cookies as well). Stir them into the dough till mixed evenly.
Measure out the dough to be 3.5 oz (about 6 TBS) and separate that dough into 2 sections.
Press the bottom of a Tablespoon into one half of the dough to make an indent. Then fill the indent with about 2 tsp (a little less than a Tablespoon) of cookie butter.
Use the other half of the dough to cover the cookie butter, and pinch the dough together to seal. Roll it into a ball, and place it onto the prepared cookie sheet.
Top the cookie dough ball with a few white chocolate chips and Biscoff cookie pieces.
Repeat and place 6 large cookie balls onto the cookie sheet.
Bake in the preheated oven for about 8-10 minutes, until the tops of the cookies, are set and golden. I usually pull mine out at 8 minutes.
Remove from the oven and let the cookies cool on the pan for about 10 minutes.
Then transfer the cookies to a cooling rack to cool completely, or enjoy them warm.