Preheat your oven to 180°C (350°F). Line a muffin tin with paper liners or grease it well to prevent sticking.
In a large mixing bowl, whisk together the all-purpose flour, baking powder, salt, and sugar until evenly combined. This creates a light, airy dry base for your muffins.
In a separate bowl, combine the peanut butter and milk, stirring until the mixture is smooth and slightly glossy. The peanut butter will melt into the liquid, filling the bowl with a warm, nutty aroma.
Add the eggs to the wet mixture one at a time, gently folding each in to create a creamy, cohesive batter. The eggs add moisture and help bind the ingredients together.
Pour the wet ingredients into the dry mixture and gently fold together using a spatula or spoon. Mix just until the ingredients are combined; avoid overmixing to keep the muffins tender. The batter should be thick but scoopable.
Spoon the batter into the prepared muffin tin, filling each cup about ¾ full. The batter will be sticky, with visible swirls of peanut butter, promising rich flavor in every bite.
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. 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. This resting period helps set the crumb and makes them easier to handle.
Transfer the muffins to a wire rack to cool completely, revealing their tender, moist texture with pockets of melted peanut butter.
Once cooled, serve the muffins warm or at room temperature. For an extra treat, drizzle with honey or sprinkle a pinch of sea salt on top before enjoying.