Preheat your oven to 180°C (350°F). Line your muffin tin with paper liners or lightly grease it to prevent sticking.
In a large mixing bowl, combine the peanut butter and sugar. Use a whisk or spoon to stir until the mixture is smooth and slightly fluffy, releasing a nutty aroma.
Add the eggs one at a time, mixing well after each addition. The batter will become creamy and thick.
Pour in the milk and vanilla extract, stirring until everything is well combined. The batter should be smooth and slightly pourable.
Sift in the all-purpose flour and baking soda into the wet ingredients. Gently fold the mixture together until just combined; avoid overmixing to keep the muffins tender.
Divide the batter evenly among the muffin cups, filling each about three-quarters full. For extra texture, sprinkle chopped peanuts on top of each muffin before baking.
Bake in the preheated oven for 15-18 minutes, or until the muffins are golden on top and a toothpick inserted into the center comes out clean.
Remove the muffins from the oven and let them cool in the tin for about 5 minutes. Then, transfer them to a cooling rack to cool completely or serve warm.
Enjoy these hearty, nostalgic muffins warm, optionally spread with butter or honey for an extra treat.