My sister begs for this sweet treat every March. Just 3 ingredients. Wrap these up in little silver packets and let them bake to perfection your guests will go crazy over what is inside.

Every March, when the snow along our fence line starts to melt into gray slush and the red-winged blackbirds come back to the cattails, my sister starts calling to ask if I’ve made “those little silver packets” yet. She means these slow cooker white chocolate blondies, wrapped up snug in foil like tiny presents and left to bake low and slow until they turn fudgy and fragrant. The recipe is as simple as can be—just three pantry ingredients—and it reminds me of the church ladies’ bar recipes from the 1970s, only easier. You tuck the batter into individual foil packets, pile them into a warm slow cooker, and let the gentle heat do the rest. When you open the foil, the soft blondies with their melty white chocolate centers feel like a surprise, even if you’ve made them a hundred times.

Serve these warm, straight from their foil packets, dusted with powdered sugar right before they hit the table. A scoop of vanilla ice cream or a dollop of whipped cream turns them into an old-fashioned supper-club style dessert. They go nicely with coffee after Sunday dinner, or with cold milk for the grandkids at the kitchen table. If you’re hosting a little gathering, keep the blondies in the slow cooker on warm and let guests open their own foil packets—set out small plates, forks, and maybe a bowl of fresh berries to cut the sweetness just a bit.

Servings: 8–10 blondies

1 box (about 15.25–16.5 oz) yellow cake mix

Prepare the slow cooker and foil packets: Line the bottom of a 5- to 6-quart slow cooker with a piece of parchment paper or a single layer of foil for easier cleanup (no need to grease). Tear off 8–10 pieces of aluminum foil, each about 8 inches square. These will be your little silver packets.

Mix the simple blondie batter: In a medium mixing bowl, add the dry yellow cake mix. Pour in the melted, slightly cooled butter. Stir with a sturdy spoon until the mixture comes together into a thick, soft dough; it will be stiffer than cake batter and closer to cookie dough. Fold in the white chocolate chips until evenly distributed.

Shape the blondies: Divide the dough evenly among the prepared foil squares, placing a mound of dough in the center of each piece. Aim for 8–10 equal portions so they cook at the same rate. Gently pat each mound into a thick round or rectangle, about 1/2 to 3/4 inch thick.

Wrap into little silver packets: Bring the sides of each foil square up and over the dough, folding the edges together at the top to seal. Then fold in the ends so each blondie is snugly wrapped. You want them sealed but not squeezed too tightly so the dough has room to puff slightly.

Arrange in the slow cooker: Place the foil packets in the slow cooker in a single layer if possible, seam side up. If you need to stack a few on top, that’s fine—just try to keep them in an even layer and not packed too tightly. Cover the slow cooker with the lid.

Cook low and slow: Cook on LOW for 2 to 2 1/2 hours, or until the blondies feel set when you gently press the top of a packet with your fingers or a spoon. They should feel firm around the edges but still slightly soft in the center. If your slow cooker runs hot, begin checking around 1 hour 45 minutes.

Rest before serving: Turn off the slow cooker and let the foil packets sit, covered, for 10–15 minutes. This resting time helps the blondies finish setting and keeps the centers soft and fudgy, not dry.

Serve the surprise: Carefully lift the warm foil packets from the slow cooker and place them in a red slow cooker insert or on a tray if you’re serving buffet-style. Open each packet just before serving, or let guests open their own. If you like, dust the tops of the blondies with a light sprinkle of powdered sugar for a pretty finish, just like a little snowfall on top.

Store leftovers: Let any leftover blondies cool completely in their foil. Store the wrapped packets in an airtight container at room temperature for up to 3 days. To rewarm, place the foil packets back into the slow cooker on LOW for 20–30 minutes, or warm briefly in a low oven until soft.

For a slightly chewier blondie, use only 7 tablespoons of melted butter instead of a full 1/2 cup; the dough will be a bit drier, but it bakes up with more chew. If you like a stronger vanilla flavor, stir 1 teaspoon vanilla extract into the melted butter before mixing it with the cake mix (this doesn’t change the basic 3-ingredient nature much, but you can skip it if you’re a purist). You can also shape the dough into smaller mounds for bite-sized packets; just reduce the slow cooker time by 15–20 minutes and start checking early. For neater edges, lightly chill the dough for 15–20 minutes before portioning so it’s easier to shape. If your slow cooker tends to trap too much moisture and make baked goods damp, place a clean kitchen towel under the lid (with the ends flipped up over the lid so they don’t touch the heating element) to absorb excess condensation. To dress them up for company, serve the opened foil packets right in a red slow cooker insert, dusted with powdered sugar and paired with a scoop of ice cream or a drizzle of caramel sauce. And if you’re baking for a crowd, you can double the recipe and cook in batches, keeping finished packets warm on the LOW or WARM setting until everyone has arrived.