Preheat & Prep: Preheat your oven to 375°F (190°C). Line a muffin tin or grease it well—no one wants muffins stuck forever.
Mix Dry Ingredients: In a large bowl, whisk together flour, sugar, baking powder, and salt. Simple, quick, done.
Mix Wet Ingredients: In another bowl, whisk milk, peanut butter, oil, egg, and vanilla until mostly smooth. Small peanut butter lumps are totally fine.
Combine: Pour wet ingredients into the dry ingredients. Stir gently until just combined. Do not overmix—lumpy batter = tender muffins.
Fill & Swirl: Spoon batter into muffin cups, filling them about ¾ full. Drop a teaspoon of jelly into each and gently swirl with a toothpick.
Bake: Bake for 18–22 minutes until tops are lightly golden and a toothpick comes out mostly clean. Jam streaks are acceptable—and encouraged.
Cool (Briefly): Let muffins cool for 5 minutes before removing. Or don’t, and burn your tongue. Your call.