Sourdough Oatmeal Cream Pie Bars
Soft, spiced sourdough oatmeal cookie baked as two sheet pan slabs and sandwiched around a marshmallow creme filling, then cut into bars. All the flavor of individual oatmeal cream pies with none of the scooping, shaping, or piping.
Servings: 24 Bars
Calories: 394kcal
Equipment
- 2 Quarter sheet pans
- kitchen scale
- Stand mixer with paddle attachment
- Food processor or blender, for grinding the oat flour
- Mini rolling pin
- Small offset spatula
- Cookie scoop, for portioning the filling optional
- Wire cooling racks
- Parchment paper
- plastic wrap
- Long sharp chef knife
- A flat board or upturned sheet pan, for flipping the top slab
Ingredients
Oatmeal Slabs
- 283 g unsalted butter softened (1 1/4 cups)
- 265 g dark brown sugar packed (1 1/4 cups)
- 100 g granulated sugar 1/2 cup
- 30 g molasses unsulphured or blackstrap (1 1/2 Tbsp)
- 2 large eggs plus 1 large egg yolk about 118 g
- 12 g vanilla extract 1 Tbsp
- 160 g sourdough discard 100% hydration (2/3 cup)
- 330 g all purpose flour 2 3/4 cups
- 180 g old fashioned rolled oats left whole (2 cups)
- 60 g old fashioned rolled oats ground to a flour (2/3 cup, measured before grinding)
- 6 g baking soda 1 tsp
- 2 g baking powder 1/2 tsp
- 7 g fine sea salt 1 1/4 tsp
- 5 g ground cinnamon 2 tsp
- 0.5 g ground nutmeg 1/4 tsp
Marshmallow Creme Filling
- 198 g unsalted butter softened (1 3/4 sticks)
- 68 g shortening 1/3 cup
- 198 g marshmallow creme one 7 oz jar
- 170 g powdered sugar 1 1/2 cups
- 8 g vanilla extract 2 tsp
- 3 g fine sea salt 1/2 tsp
Instructions
- Grind the 60 g of oats in a food processor or blender until they look like a coarse flour. Whisk together with the all purpose flour, whole oats, baking soda, baking powder, salt, cinnamon, and nutmeg. Set aside.
- Cream the butter with both sugars and the molasses on medium with the paddle for a full 4 minutes, scraping down twice, until pale and light. Do not shorten this step.
- Add the eggs one at a time, then the yolk, beating well after each. Add the vanilla and the sourdough discard and mix until smooth and glossy.
- Add the dry mixture all at once and mix on low just until no dry flour remains. The dough will be thick and sticky. This is correct. Do not add extra flour.
- Cover the dough and refrigerate at least 2 hours, or up to 48 hours for a longer ferment. This chill is required, not optional. The dough is too sticky to handle straight from the mixer.
- Line two quarter sheet pans with a parchment sling that hangs over the two long sides. Do not grease underneath.
- Weigh 780 g of chilled dough into each pan or weigh your dough ball and divide by 2 for more accurate results, dropping it in six or eight separate blobs spread around rather than one mound in the center.
- Lay a sheet of plastic wrap loosely over the dough and roll it level right in the pan with a small rolling pin, working the corners deliberately. The dough will be where you put it, so if its thicker in spots before baking, it will be thicker there after baking. Peel the plastic away.
- Heat the oven to 350°F (175°C).
- Bake 18 to 22 minutes, checking at 18. Pull when the edges are set and just releasing from the parchment and the center still looks slightly underdone. It will not look finished. Take it out anyway.
- Rap each pan firmly on the counter once or twice the moment it leaves the oven to settle any doming.
- Cool 10 minutes in the pan, then lift both slabs out by the parchment onto racks and cool completely.
- Beat the filling butter and shortening together until smooth and light, about 2 minutes. Add the marshmallow creme and beat 1 minute more. Add the powdered sugar, vanilla, and salt, then whip on medium high 2 minutes until fluffy.
- Chill both cooled slabs in the refrigerator 30 minutes. Invert the first slab onto a board so the craggy baked side faces down and the smooth pan side faces up, then peel off the parchment.
- Scoop the filling across the slab in dollops and spread it into an even layer right out to the edges.
- Lay parchment over the second slab, set a flat board on top, and flip it so the slab is craggy side down. Peel off the parchment underneath, flip once more onto a second board so it is craggy side up, then line up one long edge and slide it onto the filling while drawing the board back out.
- Press gently with a flat sheet pan to seat and level everything.
- Cover with plastic wrap and freeze 1 hour.
- Cut while still frozen. Trim 1/4 inch from all four sides, then cut 4 columns down the length and 6 rows across the width. Press straight down rather than sawing and wipe the blade between cuts.
- Let the bars sit at room temperature 20 to 30 minutes before serving.
Notes
No Sourdough Starter
Leave out the 160 g of sourdough discard and add 80 g all purpose flour (2/3 cup) and 90 g whole milk (6 Tbsp) in its place. Nothing else changes, both leaveners included. Total dough comes to about 1569 g, so weigh 785 g into each pan. Milk works better than water here because it puts back the liquid and adds fat and milk sugars on top, which means a more tender bar and better browning. Start checking at 18 minutes, since those milk sugars brown faster.
The Chill Is Required
This dough is genuinely sticky and will not roll out straight from the mixer. It needs at least 1 to 2 hours in the refrigerator to be workable. You can chill it in the bowl, wrapped as two flattened discs, or already weighed into the lined pans and covered. Do not skip it and do not fix the stickiness with extra flour, since every gram of flour there comes back as a drier, tougher bar.
Rolling It Out Ahead
Weigh the chilled dough into both lined pans, roll it level under plastic wrap, then leave the plastic right on top and put the pans back in the refrigerator overnight. The next morning they go straight from refrigerator to oven with nothing left to do.
Which Side Faces Out
The craggy baked tops face outward on the finished bar and the two smooth pan sides meet in the middle against the filling. Built the other way you get two flat faces and it reads like a snack cake rather than an oatmeal cream pie.
Baking Two Pans
Bake the first pan on its own, note what it actually needed, and run the second to that time. Room temperature dough finishes near 18 minutes and refrigerated dough near 22.But ever oven is different.
Storage
Cut bars keep airtight at room temperature for 3 days. There is no fresh dairy in the filling, so they do not need the refrigerator. The assembled slab also freezes excellently, and the bars are very good eaten straight from frozen. Unfilled slabs freeze up to 2 months.
