Preheat your oven to 180°C (350°F) and line a muffin tin with paper liners or lightly grease it.
In a mixing bowl, combine the creamy peanut butter and sugar, then beat with a spatula until smooth and fragrant, about 1-2 minutes.
Add the eggs one at a time, whisking well after each addition until the mixture is creamy and slightly fluffy.
Sift in the all-purpose flour, baking powder, and salt into the wet mixture, then gently fold everything together with a spatula until just combined—avoid overmixing to keep the muffins tender.
Stir in the milk gradually, just until the batter is slightly loosened and creamy, about 1-2 tablespoons at a time.
Spoon the batter into the prepared muffin cups, filling each about 3/4 full. Add a tiny pinch of sea salt or a peanut half on top for extra flavor if desired.
Bake in the preheated oven for 18-20 minutes, until the tops turn a golden brown and a toothpick inserted in the center comes out clean.
Remove the muffins from the oven and let them cool in the tin for about 5 minutes, then transfer to a wire rack to cool completely. The muffins will be moist, fragrant, and slightly cracked on top.
Enjoy these warm and comforting muffins, perfect for a quick breakfast or a nostalgic snack.