Preheat oven to 350°. Line 1 to 2 mini muffin pans with 28 mini paper baking liners.
In a medium bowl, stir together brown sugar, peanut butter, and oil until well combined. Whisk in egg and vanilla until well combined.
In a separate medium bowl, sift together flour, baking powder, and baking soda. Whisk in salt. Gradually add flour mixture to brown sugar mixture, alternately with buttermilk, beginning and ending with flour mixture, and stirring just until combined. Spoon batter into prepared muffin cups (about 1 tablespoon each).
Bake until a wooden pick comes out clean, about 8 minutes. Let cool in pan for 5 minutes. Remove from pan and let cool completely on a wire rack.
Using a wooden pick, make a ¼-inch-wide hole in the center of each cupcake top. Using a small piping bag fitted with a ¼-inch round pastry tip, pipe jam evenly into cupcakes.
Using a small piping bag fitted with a medium open star tip, pipe Strawberry Jam Frosting evenly over cupcakes.
Recipe by Southern Lady Magazine at https://southernladymagazine.com/mini-peanut-butter-jelly-cupcakes-recipe/