In a ramekin, stir together the flax meal and water. Allow to rest for 10 minutes and mix every now and then to make sure it combines. This mixture is your "flax egg."
Add the all-purpose flour, corn starch, baking soda, and salt into a large bowl, and mix well. Set aside.
To a standing mixer, add the butter, brown sugar, cane sugar, vanilla extract, and the flax egg. Using the paddle attachment, beat this on medium-high speed for 3 minutes, until light and fluffy. Stop the standing mixer and scrape down the sides of the bowl as needed.
Change the mixer's speed down to low and gradually pour the flour mixture inside, about 1/2 cup at a time. Mix until everything is combined, and it has formed into a dough.
Once a dough has formed, turn the mixer off, and add in the chocolate chip chunks and marshmallows. Carefully stir with a rubber spatula until evenly combined.
Now, press a sheet of plastic wrap directly onto the dough and set it in the refrigerator to chill for 30 minutes.
Line 2 large sheet pans with a piece of parchment paper.
Once the dough has chilled and is easy to handle, measure out 2 tablespoon portions for each cookie.
Break up 1 Biscoff cookie into 5 pieces and press it into a cookie dough ball. Repeat with all balls of dough. (Each ball of dough gets 1 whole, crushed, Biscoff cookie.)
Set the cookie dough balls onto the prepared baking sheets, making sure to leave about 2 inches all around each cookie, as they will spread out a bit as they bake.
Press 3 more chocolate chunks onto the tops of each cookie dough ball for decoration purposes.
Place the sheet pans of cookie dough into the freezer for 10 minutes or into the refrigerator for 30 minutes, to slightly chill.