Step 1

Butter an 8-inch square baking pan then line with a piece of parchment paper with the 2 sides overhanging for easy removal.

Step 2

Put butter and peanut butter in a large bowl and microwave until both are melted and liquid, about 3 minutes. Whisk until thoroughly combined.

Step 3

Stir in the vanilla and salt, if using.

Step 4

Add the powdered sugar and stir until no white streaks remain.

Step 5

Press the fudge into the prepared pan and smooth with a spatula. If you’d like a swirly pattern on top, press the edge of a spoon around the surface.

Step 6

Let cool to room temperature then cover and refrigerate for 4 hours until set and firm.

Step 7

Cut into squares.

Step 8

Store in an airtight container at room temperature for a week, or 2-3 weeks in the refrigerator.