Ingredients
Scale
The Brownie Batter
- ½ cup (115g) unsalted butter, cut into pieces
- 4 oz (115g) dark chocolate (60–70% cacao), roughly chopped
- 1 cup (200g) granulated sugar
- ¼ cup (50g) packed brown sugar
- 3 large eggs, at room temperature
- 1 tsp pure vanilla extract
- ½ cup (50g) Dutch-process cocoa powder
- ¾ cup (95g) all-purpose flour
- ½ tsp salt
- 1 tsp espresso powder (optional)
The Peanut Butter Swirl
- ½ cup (130g) creamy peanut butter
- 3 tbsp powdered sugar
- 1 tbsp unsalted butter, melted
- Pinch of salt
To Finish
- Flaky sea salt, for scattering over the top
- Optional: powdered sugar for dusting
To Serve
- Vanilla ice cream
- Hot fudge or caramel sauce
- Whipped cream
Instructions
- Prepare the slow cooker. Line the slow cooker insert with parchment paper, pressing it into the bottom and up the sides with some overhang for handles. Grease the parchment lightly with butter or cooking spray. Set aside.
- Melt the chocolate and butter. In a medium saucepan over low heat, melt the butter and chopped dark chocolate together, stirring constantly, until completely smooth. Alternatively, melt in a microwave-safe bowl in 30-second intervals, stirring between each. Remove from heat and let cool slightly — about 5 minutes.
- Add the sugars. Whisk the granulated sugar and brown sugar into the warm chocolate mixture until fully combined.
- Add the eggs and vanilla. Add the eggs one at a time, whisking well after each addition until fully incorporated and the batter is smooth and glossy. Stir in the vanilla extract.
- Add the dry ingredients. Sift the cocoa powder, flour, salt, and espresso powder (if using) directly into the chocolate mixture. Fold with a rubber spatula until just combined — do not overmix. A few small streaks of flour are fine; they will incorporate during cooking. The batter will be thick and glossy.
- Make the peanut butter swirl. In a small bowl, stir together the peanut butter, powdered sugar, melted butter, and salt until smooth and slightly loosened.
- Assemble. Pour the brownie batter into the prepared slow cooker and spread into an even layer with a spatula. Drop heaped teaspoons of the peanut butter mixture over the surface of the batter in roughly 8–10 evenly spaced dollops. Using a butter knife or skewer, drag through the dollops in long, sweeping S-shapes or figure-eights to create a swirl pattern. Do not over-swirl.
- Set up the slow cooker. Lay 2 full sheets of paper towels flat across the top of the slow cooker opening. Place the lid on top, securing the paper towels between the lid and the slow cooker rim to absorb condensation.
- Cook. Set the slow cooker to HIGH. Cook for 2 to 2.5 hours without lifting the lid. Begin checking at the 2-hour mark. The brownies are done when the edges are set and pulling slightly away from the sides, the top has a matte, set appearance, and the very center has a slight wobble but does not look wet or liquid when the insert is gently shaken.
- Finish with flaky salt. Immediately after cooking, scatter a generous pinch of flaky sea salt evenly over the surface while the brownies are still hot.
- Cool completely. Turn off the slow cooker and remove the insert. Allow the brownies to cool in the insert for 30 minutes, then use the parchment paper handles to lift the entire brownie slab out onto a wire rack. Cool to room temperature completely before slicing — at least 1 hour. For the cleanest, most defined slices, refrigerate for 1 hour after reaching room temperature.
- Slice and serve. Using a sharp knife dipped in hot water and wiped dry between each cut, slice into squares. Serve at room temperature, or warm briefly in the microwave for 15–20 seconds and top with a scoop of vanilla ice cream.
Notes
- Do not overbake. The most common slow cooker brownie mistake is cooking them until the center looks completely firm. A slight wobble in the center when done is correct — the brownies continue to set as they cool. Overbaked slow cooker brownies are dry and lose their signature fudginess entirely.
- The paper towel trick is non-negotiable. Condensation dripping onto the brownie surface during cooking creates wet, steamed patches that ruin the texture of the top. Two paper towels under the lid solve this completely — use them every time.
- Cool before cutting. Warm brownies pull apart and smear — they look and taste much better when fully cooled and properly set. If patience is difficult, the fridge speeds this up significantly.
- Espresso powder is the secret ingredient. It does not make the brownies taste like coffee. It deepens and intensifies the chocolate flavor in a way that is immediately noticeable but impossible to pinpoint. Use it.
- Natural vs conventional peanut butter. Natural peanut butter has better flavor but must be well-stirred before using. Conventional peanut butter is more stable and slightly sweeter. Both work beautifully.
- Slow cooker size and timing. A 6-quart oval slow cooker produces brownies approximately 1.5 inches thick — ideal. A smaller insert will produce thicker brownies that need more time; a larger insert will produce thinner brownies that cook faster. Adjust timing accordingly and always use the wobble test rather than a fixed time.
- Flaky salt is not optional. The scatter of flaky sea salt over hot brownies is one of the single best finishing touches in all of baking. It costs almost nothing and makes a profound difference.
- Prep Time: 20 minutes
- Cook Time: 2 hours 15 minutes (on HIGH)
- Category: Dessert
- Method: Slow Cooking
- Cuisine: American