1. Preheat the oven to 350 degrees f.
2. Line the bottom of a square 8 inch x 8 inch non stick baking pan with parchment paper.
3. In a large bowl with an electric mixer or stand mixer with paddle attachment, combine dry ingredients.
4. In a medium bowl cream together butter and sugar. Add eggs and vanilla and mix well.
5. Add the wet ingredients to the dry ingredients and mix until a smooth batter forms.
6. Fold in mashed bananas and optional ingredients.
7. Pour the batter into the square baking pan.
8. Bake for 30-35 minutes until golden brown or until a toothpick inserted comes out clean.
Tip: slightly under bake the bars for a softer texture in the center.
9. Remove to a wire rack to completely cool.
10. Cut into 2 inch bars for serving.