Most slow-cooker cakes are served with a spoon. This one is built to be sliced, and every structural decision follows from that: a pressed crumb base, a parchment sling wide enough to lift by, and two hours in the fridge before a knife goes near it.
The layers go on in stages as the thing cools. Marshmallow creme onto a cake that has already rested twenty minutes, ganache over that, and the loose garnish only after the chill.
Why This Recipe Works
- Pressing the graham crumbs firmly gives a base solid enough to support three layers above it.
- A towel under the lid keeps condensation off the cake layer while it sets.
- Letting the cake cool twenty minutes before the marshmallow creme stops it melting straight into the crumb.
- Chilling two hours firms the ganache and the creme into distinct layers rather than a single soft mass.
Ingredient Notes
- Graham cracker crumbs, twice
- A cup and a half pressed into the base, and a third of a cup scattered on top after chilling.
- Mini marshmallows, divided
- A cup and a half: one cup into the marshmallow layer, the rest scattered on at the very end so they stay round.
- Semisweet chocolate and cream
- Eight ounces chopped and three-quarters of a cup, made into a ganache rather than melted alone.
How to Make It
Sling, then crust
Line a 6-quart slow cooker with a wide parchment sling and grease it. Mix graham crumbs, butter and brown sugar; press firmly into the bottom.
Cake layer, under a towel
Mix cake mix, eggs, oil and milk and spread over the crust. Cook on High 2 to 2 1/2 hours with a towel under the lid, until the cake layer is set.
Cool, then marshmallow
Cool 20 minutes in the cooker. Spread marshmallow creme over the cake and scatter with 1 cup mini marshmallows.
Make and spread the ganache
Heat cream until steaming, pour over chocolate, rest 2 minutes, and stir smooth. Spread ganache over the marshmallow layer.
Lift, chill, finish
Lift out with parchment, chill at least 2 hours until sliceable, then finish with remaining mini marshmallows and graham crumbs.
The Four Layers of the Slice
Each layer goes on only once the one beneath it is cool or firm enough to take it. Rushed, they merge into a single soft mass and the slice disappears.
The ganache
8 oz of chopped semisweet chocolate with 3/4 cup of steaming cream, rested 2 minutes and stirred smooth, spread over the marshmallow. It firms in the fridge into the thick dark top the slice shows.
The marshmallow layer
A 7 oz jar of marshmallow creme spread over the cake after a 20-minute cool, scattered with 1 cup of mini marshmallows. Spread onto a hot cake it would simply melt into it.
The cake
A 15.25 oz box mix with eggs, oil and milk, spread over the crust and cooked 2 to 2 1/2 hours on HIGH under a towel, until set with no wet batter.
The graham base
1 1/2 cups of crumbs with 6 tbsp melted butter and 2 tbsp brown sugar, pressed FIRMLY into the lined cooker. Everything above it is soft, so this is the layer that makes a slice possible.
Success Tips
- Make the parchment sling wide enough to grip on both sides — the finished slab is heavy.
- Press the crumb base firmly; a loose crust crumbles when you cut through the layers.
- Do not shortcut the chill. Two hours is what turns this from a scoop into a slice.
Serving Ideas
Ten servings, cut from the chilled slab so each shows the graham base, the white marshmallow layer and the ganache top, finished with mini marshmallows and crumbs.
Frequently Asked Questions
Can I serve it warm?
Not as this recipe is written. The two-hour chill is what makes it a sliceable layered slab rather than a scoopable crock cake.
Why a towel under the lid?
It catches the condensation a sealed cooker makes, which would otherwise fall onto the cake layer.
How do I know the cake layer is ready?
It should be fully set with no wet batter before any topping goes on.
