Oatmeal Sandwich Cookies

For the cookies:
Preheat the oven to 350 F. In a large bowl, cream the butter and brown sugar. Then mix in the egg and vanilla. Mix in the oats, flour and baking soda just until combined. Measure the dough with a tablespoon-sized cookie dough scoop, but fill the scoop just almost all the way full. Place the scoops of dough on cookie sheets that you've covered in parchment paper. You should have 26 cookies. Bake for 14 minutes, swapping the position of the pans halfway through to ensure even cooking. Remove pans from the oven and let cookies cool completely (not on a cooling rack) before filling them.
For the filling:
Using a handheld mixer beat the egg white and sugar just until creamy, white and slightly increased in volume. Add the mascarpone and beat the mixture until it becomes thickened and creamy and has the appearance of frosting.
Match up the cookies in pairs according to their size and shape and smear one of the cookies from each pair with a dab of the filling. This recipe makes a little extra filling, and be conscious of how much you are using. But it isn't rocket science, so don't think too much about it. Top the filled cookie with its partner and repeat with the rest of the cookie pairs. Enjoy!