1/2 cup (120 milliliters) butter + extra for greasing baking dish
1/4 cup (60 milliliters) milk
1 teaspoon (5 milliliters) vanilla
1/2 cup (120 milliliters) cocoa powder
2/3 cup (160 milliliters) sugar
3/4 cup (180 milliliters) flour
1/4 teaspoon (1 milliliters) salt
Add peanut butter to a small microwave-proof bowl and melt in the microwave. Set aside.
Add butter to a large microwave-proof bowl and melt in the microwave. Set aside.
In a bowl, whisk together eggs, milk, vanilla, cocoa, melted butter, sugar, flour, and salt. Pour mixture into a greased microwave-proof baking dish. Drizzle melted peanut butter on top and use a butter knife to swirl a pattern on top with the peanut butter. Microwave on medium-high for seven to eight minutes. Let cool.