Preheat your oven to 180°C (350°F) and line a muffin tin with paper liners or grease it well.
In a large mixing bowl, whisk together the flour, brown sugar, and baking powder until evenly combined. This helps distribute the leavening agents for a good rise.
In a separate bowl, beat the egg, then stir in the milk, melted butter, and creamy peanut butter until the mixture is smooth and slightly frothy. This creates a rich, cohesive wet base.
Pour the wet mixture into the bowl of dry ingredients, gently folding together with a spoon or whisk. Mix until just combined; avoid overmixing to keep the muffins tender.
Spoon the batter into the prepared muffin cups, filling each about two-thirds full. Use the back of the spoon to smooth the tops and create an even surface.
If desired, add a small dollop of peanut butter in the center of each muffin for gooey pockets, or swirl gently with a toothpick.
Bake in the preheated oven for 18-20 minutes, until the muffins are golden and cracked on top, and a toothpick inserted into the center comes out clean.
Once baked, 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 slightly, which prevents sogginess.
If desired, drizzle with honey or sprinkle with sea salt for extra flavor. Serve warm or at room temperature for best taste.
