Prep the pan: Line an 8x8-inch pan with parchment paper, leaving overhang on two sides to lift out later. Lightly mist with nonstick spray if your parchment slides.

Melt the base: In a microwave-safe bowl, add 1/2 cup peanut butter and 1/3 cup coconut oil. Microwave in 20–30 second bursts, stirring between each, until just melted and smooth. Alternatively, warm gently on the stovetop over low heat.

Whisk in flavor: Add cocoa powder, vanilla, salt, and sweetener. Whisk until glossy and fully combined.

Add protein powder: Sprinkle in the protein powder gradually, whisking to prevent lumps. The mixture should be thick but pourable. If it’s too thick, whisk in 1–2 tablespoons of warm water or milk (dairy or non-dairy) to loosen.

Taste and adjust: Sweetness can vary depending on protein powder and cocoa. Add another tablespoon of sweetener or a pinch of salt if needed.

Pour and level: Pour the chocolate fudge mixture into the lined pan. Tap the pan on the counter to pop air bubbles and smooth the top.

Create the swirl: Warm the extra 2 tablespoons of peanut butter for 10–15 seconds so it’s runny. Drizzle over the surface in thin lines. Use a toothpick or knife to drag gentle S-shapes through the peanut butter to create swirls. Don’t overmix—clean lines look best.

Optional add-ins: Sprinkle on chopped peanuts or mini chips and lightly press to set.

Chill: Refrigerate for 1.5–2 hours, or until firm enough to slice. For faster setting, place in the freezer for 30–40 minutes, then transfer to the fridge.

Slice and serve: Lift the slab out using the parchment. Warm a sharp knife under hot water, dry, and cut into 16–25 squares, depending on your preferred size.