Preheat the oven to 325°F
Combine the flour, baking powder, sea salt, and cinnamon in a bowl and set aside
In a separate bowl, cream the butter, egg, stevia, and stevia brown sugar together with a hand mixer*
Incorporate the vanilla, syrup, yogurt, and peanut butter into the butter and egg mixture
Mix the dry ingredients into the wet until it's smooth and clump-free
Evenly spread the batter into a prepared 8x8 or 9x9 baking pan
Make 4 evenly spaced parallel lines of Nutiva or Nutella across the batter
Lightly drag a butter knife through the batter in the opposite direction of the Nutiva or Nutella lines to create swirled lines
Bake for 20-22 minutes or until the edges are golden brown – it’s okay if the middle isn’t fully cooked, the bars will continue to cook as they cool
Sprinkle flaky sea salt on top of the bars (optional) and let cool before cutting into 12 equal squares