Step 1: Prepare the Brownie Batter

1. In a medium mixing bowl, combine 18.3 oz chewy fudge brownie mix, ½ cup vegetable oil, ¼ cup water, and 2 beaten large eggs. Stir with a spatula until just combined, avoiding overmixing to maintain a fudgy texture.

   • Tip: Use room-temperature eggs for better emulsification. Stir gently to prevent a tough texture. Scrape the bowl to ensure all ingredients are incorporated.

Step 2: Prepare the Slow Cooker

1. Lightly grease a 4-6 quart slow cooker insert with cooking spray or a thin layer of butter to prevent sticking.

2. For easier removal, line the slow cooker with a parchment paper sling (two long strips crossed, overhanging the edges) and lightly spray the parchment.

   • Tip: Use a slow cooker liner or parchment sling for easy cleanup and removal. Ensure the insert is evenly greased to avoid sticking.

Step 3: Layer the Batter and Peanut Butter Cups

1. Pour half the brownie batter into the slow cooker, spreading it evenly with a spatula.

2. Arrange 12 miniature Reese’s peanut butter cups (or 6 full-size, halved) evenly over the batter, pressing them lightly into the surface.

3. Pour the remaining brownie batter over the peanut butter cups, smoothing the top to cover them completely.

   • Tip: Space peanut butter cups evenly to ensure each serving has a peanut butter burst. Spread the top layer gently to avoid disturbing the cups.

Step 4: Slow Cook

1. Cover and cook on low for 2-3 hours or high for 1.5-2 hours, until the edges are set and a toothpick inserted in the center comes out with moist crumbs (not wet batter).

2. Check doneness at the minimum time; if the center is too wet, continue cooking in 15-minute increments. If the top looks too moist, remove the lid for the last 15-20 minutes to evaporate excess moisture.

   • Tip: Place a paper towel or clean dish towel under the lid to catch condensation and prevent a soggy surface. Avoid lifting the lid too often to maintain heat. Cooking times vary by slow cooker model.

Step 5: Prepare the Peanut Butter Frosting

1. In a medium mixing bowl, use a handheld mixer or stand mixer on medium-high speed to beat ¾ cup softened salted sweet cream butter, 1 ¼ cups creamy peanut butter, and 1 ½ tsp pure vanilla extract for 1 ½ to 2 minutes, until smooth and creamy.

2. Add 2 ¼ cups powdered sugar, ½ cup at a time, alternating with 3-5 tbsp whole milk, beating until fully incorporated and the frosting is smooth and spreadable. Adjust milk for desired consistency.

   • Tip: Soften butter at room temperature for easier beating. Add milk gradually to avoid a runny frosting. Beat until fluffy for a professional finish.

Step 6: Cool and Assemble

1. Turn off the slow cooker and let the brownie cake cool in the insert for 10-15 minutes to set slightly, making it easier to remove or scoop.

2. Use the parchment sling (if used) to lift the cake out, or scoop portions directly from the slow cooker. Transfer to a serving platter if slicing, or serve warm from the slow cooker for a rustic presentation.

3. Spread or pipe the peanut butter frosting over the cooled or slightly warm cake using a spatula or piping bag with an open star tip. For piping, hold the bag ½ inch above the surface and swirl in a C-shape to create a star swirl effect.

4. Sprinkle 1 ½ cups Reese’s minis over the frosted cake for garnish.

   • Tip: Cool the cake slightly before frosting to prevent melting. Pipe frosting for a decorative look or spread for simplicity. Scatter Reese’s minis evenly for visual appeal.

Step 7: Serve

1. Slice the cooled cake into 8-10 squares or wedges, or scoop warm portions into bowls or dessert cups (about ½ cup per serving).

2. Serve warm for a gooey, indulgent experience or at room temperature for a firmer texture. Pair with coffee, milk, or a dessert liqueur (like Baileys) for a decadent vibe.

   • Tip: Serve in shallow bowls if scooping warm, or on plates if slicing cooled. Garnish with extra Reese’s minis or a dusting of powdered sugar for flair. Offer extra frosting or chocolate syrup on the side for customization.