In medium-sized bowl, combine peanut butter and softened butter and beat to a cream well.
Add Truvia and cream together until light and fluffy.
Whisk the eggs in a small bowl, and add to butter/sugar mixture, adding the vanilla and beat well.
In sifter or sieve, combine flour, cocoa, baking powder, and baking soda (if you don't have a sifter, that's alright, I don't have one myself). Add dry ingredients into peanut butter mixture; add milk, and stir until batter is smooth.
Spoon batter into prepared muffin cups.
Bake for 20-25 minutes or until muffins spring back when touched in center.
Remove to wire racks or plate to cool.
Makes 12-18 muffins (depending upon how full you fill each cup. I made 18 with this recipe).