Preheat your oven to 180°C (350°F) and line your muffin tin with paper liners or lightly grease it.
In a large mixing bowl, combine the peanut butter and sugar, stirring until the mixture is smooth and creamy with a slightly glossy sheen.
Add the eggs one at a time, mixing well after each addition. You'll notice the mixture becoming lighter and slightly fluffy as the eggs incorporate.
In a separate bowl, whisk together the flour, baking powder, and a pinch of salt. Gradually fold this dry mixture into the wet ingredients, just until combined—don’t overmix, to keep the muffins tender.
Pour in the milk and vanilla extract, gently folding until the batter is smooth and slightly thickened. It should be easy to scoop but still moist.
Divide the batter evenly among the muffin cups, filling each about three-quarters full. You can use an ice cream scoop for neat, even portions.
Bake the muffins for 20 to 22 minutes, or until the tops are golden brown and a toothpick inserted in the center comes out clean. You'll hear a gentle sizzle as they bake, and the aroma of roasted peanuts will fill your kitchen.
Remove the muffins from the oven and let them cool in the tin for about 5 minutes. Then transfer them to a wire rack to cool completely, which helps prevent sogginess and keeps the tops nicely domed.
Once cooled, enjoy these muffins warm or at room temperature. They’re perfect on their own or with a smear of extra peanut butter or honey for added richness.