These peanut butter brownies made with cake mix and plain peanut butter swirls, without confectioner’s sugar, are a breeze to make! I know, anything that comes from a box is a breeze to make, but these brownies are made extra special with the Reese’s peanut butter cups tucked into the batter and the lovely peanut butter swirls on top, in fact, they are so pretty that no-one will guess you used a brownie box mix to make them. A warm brownie with ice cream is always a win, especially with the Reese’s peanut butter cup and peanut butter additions! If you would enjoy more cake mix based dessert recipes, you may enjoy Peanut Butter Brookies, Cake Mix Cookies with Caramel Frosting and Pumpkin Pie Cake.
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Reese’s Peanut Butter Swirl Brownies (made with brownie mix)
Equipment
- 13 by 9 inch baking dish (linked below)
- Cutting board (linked below)
- Mixing bowl (linked below)
- measuring cups (linked below)
- Skewer (linked below)
- Spatula (linked below)
Ingredients
- 1 18.3 oz. fudgy brownie mix (I used Duncan Hines brand)
- 2 large eggs
- 1/2 cup vegetable or canola oil
- 3 tablespoons milk *see note
- 1 cup Reese's peanut butter cups, chunked
- 1/3 cup creamy peanut butter
Instructions
Preheat oven to 325:
- Combine the brownie mix with eggs, milk and oil, mixing only until lump free and moistened. Gently fold in the chunks of Reese's peanut butter cups into the batter.
- Spread the brownie batter with Reese's peanut butter chunks into the bottom of a parchment lined (*see note) or greased 13 by 9 inch baking dish.
- Melt the peanut butter in the microwave for around 30 seconds or until bubbly on the edges (keep a close eye on the peanut butter as it melts, to prevent it from getting too hot and clumping). Using a teaspoon, spread the peanut butter over the brownie mix (horizontally) about an inch or two apart, then take a skewer and draw lines through the peanut butter going vertically also 1-2 inches apart. Or dollop the peanut butter by teaspoon onto the batter and then swirl with a skewer.
- Bake the peanut butter swirled brownies in the preheated oven for 25-30 minutes until a toothpick inserted comes out mostly clean. Allow to cool, or serve warm with ice cream. Enjoy!
Notes
Equipment needed for these Reese’s Peanut Butter Swirled Brownies:
- 13 by 9 inch baking dish I like to use my glass 13 by 9 inch baking dish, because it makes checking the sides and bottoms of baked goods for doneness easier. I also like to use parchment paper to line the baking dish with for easier removal of the brownies before cutting them.
- Cutting board A cutting board is nice to have handy for chunking those Reese’s peanut butter cups before they are added to the brownie batter.
- Mixing bowl A medium sized, stainless steel mixing bowl was my go-to for the amount these peanut butter swirled brownies produced.
- Measuring cups Measuring cups are needed to measure out the oil, peanut butter and Reese’s peanut butter cups used in this swirled brownie recipe.
- Skewer I like to use a skewer to swirl the melted peanut butter into the brownie batter. Skewers have nice pointed ends that give the neatest swirls to these brownies.
- Spatula A spatula is useful for cleaning out the bowls and getting every last drop of batter, but also useful for spreading the brownie batter evenly into the 13 by 9 inch baking dish.
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Ingredients needed for these Reese’s peanut butter swirled brownies: Fudgy brownie mix, eggs, oil, milk, peanut butter and Reese’s peanut butter cups.
Is milk really necessary?
Actually, milk is not necessary if you just prefer to use water. But, adding milk to the brownies makes them more moist and gooey because of the added fats from the milk. Milk also enhances the flavor of the brownies more so than water will. Milk is my personal preference, but the brownies will still taste great with just water.

Step 1: Combine the brownie mix with eggs, milk and oil, mixing only until lump free and moistened. Gently fold in the chunks of Reese’s peanut butter cups into the batter.
I don’t have Reese’s peanut butter cups on hand, what else can I use?
If you are a big fan of Reese’s peanut butter cups, then I suggest going out and getting some (if possible) because really, these brownies are that good with the Reese’s peanut butter cups added in. But a cup of other candies such as chunked Snickers candy bars, Reese’s Pieces, Hershey’s chocolate bars (or other chocolate chunks), Milky Ways and more could be used. Feel free to adjust the recipe to fit your preference!

Step 2: Spread the brownie batter with Reese’s peanut butter chunks into the bottom of a parchment lined or greased 13 by 9 inch baking dish.

Step 3: Melt the peanut butter in the microwave for around 30 seconds or until bubbly on the edges (keep a close eye on the peanut butter as it melts, to prevent it from getting too hot and clumping). Using a teaspoon, spread the peanut butter over the brownie mix (horizontally) about an inch or two apart, then take a skewer and draw lines through the peanut butter going vertically also 1-2 inches apart. Or dollop the peanut butter by teaspoon onto the batter and then swirl with a skewer.
What can I use if I don’t have skewers on hand?
If you do not have skewers on hand, you could also use a dinner knife or toothpick to swirl the peanut butter into the brownie batter. Feel free to be creative and no worries if the swirls don’t turn out perfectly the first time. Swirled desserts take some practice to master, but it sure is fun to play around with!
Why plain peanut butter instead of peanut butter sweetened with confectioner’s sugar?
Because of the Reese’s peanut butter cups added into the already sweet brownies, my family prefers to add plain peanut butter to balance the sweetness. I personally think that the sweetness is perfectly balanced with plain peanut butter on top, especially if you plan to serve the brownies with ice cream.

Step 4: Bake the peanut butter swirled brownies in the preheated oven for 25-30 minutes until a toothpick inserted comes out mostly clean. Allow to cool, or serve warm with ice cream. Enjoy!
Storage for these peanut butter swirled brownies:
These brownies can be kept tightly wrapped at room temperature for several days, or they can be frozen in an airtight container for several months. Simply thaw at room temperature before serving at an event or enjoying at home.

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