Line an 8×8-inch baking dish with parchment paper. Place one large and one small microwave-safe bowl on your counter.

In the large bowl combine 1 cup creamy peanut butter, 1 cup salted butter, 2 teaspoons vanilla extract, and ½ teaspoon salt.

Microwave the large bowl in 1-minute increments, stirring between each increment, until the butter and peanut butter are fully melted and the mixture is smooth and pourable.

Stir 3 ½ cups powdered sugar into the melted peanut butter mixture a little at a time until fully incorporated and the mixture becomes a smooth, fudgy dough.

Transfer the peanut butter fudge to the prepared pan and press it into an even layer. Use a butter knife to make shallow ridges or gashes across the top to create crevices for the chocolate layer.

In the small bowl combine ¼ cup semisweet chocolate chips and 3 tablespoons butter.

Microwave the chocolate bowl in 1-minute increments, stirring between each increment, until the chocolate and butter are melted and the mixture is smooth.

Stir ½ cup powdered sugar and 1 teaspoon milk into the chocolate mixture until combined. If the chocolate mixture is too thick to pour or spread, stir in the second teaspoon of milk (use 1–2 teaspoons total as needed).

Pour the chocolate mixture over the peanut butter layer and gently spread it to cover. Press lightly so the chocolate works into the ridges and crevices you made.

Refrigerate the pan for at least 3 hours, until the candy is firm. Lift the fudge from the pan using the parchment paper, cut into 1-inch squares, and store the pieces in an airtight container at room temperature for up to two weeks.