Preheat your oven to 175°C (350°F). Lightly grease a muffin tin or line with paper liners, ready for the batter.
In a large bowl, whisk together the flour, brown sugar, and baking powder until evenly combined. This creates a light, airy base for your muffins.
In a separate bowl, scoop in the creamy peanut butter and add the vegetable oil. Whisk or stir until smooth and slightly shiny, filling the room with a warm peanut aroma.
Add the eggs one at a time to the peanut butter mixture, whisking after each addition until fully incorporated. The mixture should become creamy and slightly thick.
Pour in the milk and stir gently until all wet ingredients are combined and the batter is smooth, with a slightly thick but scoopable consistency.
Gradually add the dry ingredients into the wet, folding gently with a spatula until just combined. Be careful not to overmix—lumps are okay and help keep the muffins tender.
Spoon the batter into the prepared muffin cups, filling each about three-quarters full. Tap the tin lightly on the counter to settle the batter and release any trapped air.
Bake in the preheated oven for 18–20 minutes, until the muffins are golden around the edges and a toothpick inserted into the center comes out clean.
Remove the muffins from the oven and let them rest in the tin for about 5 minutes. Then transfer them to a wire rack to cool slightly, revealing a soft, moist crumb with a tempting aroma.
Enjoy the muffins warm or at room temperature, perhaps with a drizzle of honey or a pat of butter. Their tender crumb and nutty flavor make them a cozy, satisfying treat.