Related

• Molasses and brown sugar are hygroscopic. They hold water in the cookie for days, which is what keeps a filled sandwich from going stale and hard. See Molasses and sugar in baking.
• Underbake by two minutes. The centres should look wet when the tray comes out. They set on the sheet, and a fully baked oatmeal cookie is a crisp one — a fine cookie, but the wrong one here.
• Grind half the oats. Blitzing 90 g of the oats to a rough flour gives a tighter crumb that will not shed oat flakes when you bite the sandwich.
• Marshmallow in the filling, again for softness. Straight buttercream sets firm in the fridge and squeezes out of the sides.

Makes 12 pies.

Cookies:

• 225 g unsalted butter, softened
• 250 g light brown sugar
• 100 g granulated sugar
• 2 eggs
• 40 g molasses
• 2 tsp vanilla — see Pure vanilla extract
• 280 g all-purpose flour
• 8 g baking soda
• 5 g fine salt
• 6 g ground cinnamon
• 180 g rolled oats, 90 g of them blitzed to a coarse flour

Filling:

• 170 g unsalted butter, softened
• 200 g marshmallow creme
• 300 g powdered sugar
• 2 tsp vanilla
• 3 g fine salt

Cream the butter and both sugars two minutes, beat in the eggs, molasses and vanilla. Fold in the flour, soda, salt and cinnamon, then both the whole and the ground oats.

Scoop 45 g balls, 24 of them, and bake 175 °C / 350 °F for 9–11 minutes. Pull them when the edges are set and the middles still look underdone. Cool on the tray ten minutes, then on a rack completely.

Beat the filling for three minutes until very light. Pipe about 30 g onto the flat side of half the cookies and sandwich.

• Wrap each in cling film. That is not presentation — the wrap is what keeps them soft, and it is what the factory version is doing too.
• Raisins are traditional in the cookie and controversial in the sandwich. Add 120 g if you want them.
• Keeps five days at room temperature, and the texture is best on day two.

Method and theory: Cookie recipes · cookies · oats · Molasses

Nearby: whoopie pies · monster cookies · anzac biscuits