Preheat oven to 375ºF/190ºC. Spray 12 muffin cups with nonstick cooking spray or line with muffin liners. Set aside.
In a large bowl mix together flour, baking powder, and salt. Add eggs, oil, sugar, peanut butter, milk, and vanilla extract. Using a hand mixer or a standing mixer fitted with the whisk attachment, whisk ingredients on low-medium speed just until combined.
Fill muffin cups halfway with batter. Make a small well in the center of each muffin with the back of a teaspoon and spoon in 1-2 teaspoons jam. Divide remaining batter between muffin cups. Bake for 15-20 minutes or until a toothpick inserted into the center of a muffin come out clean. Remove from oven. Allow to cool in pan for 5 minutes, then transfer to a wire rack to cool completely.
Muffins are best the same day they are made, but can be kept in an airtight container, at room temperature or in the fridge, for up to 3 days. For jumbo muffins: Fill muffin cups about ¾ full and bake for 22-27 minutes or until a toothpick comes out clean. Yield: 5-6 muffins.