Preheat oven to 350 degrees. Chop the Snickers into small pieces, place in a small bowl, and set aside.
In a large bowl, whisk together the flour, baking powder, baking soda, and salt.
In a small saucepan, melt the butter over low heat. Stir in the brown sugar until completely dissolved, then add the eggs and vanilla and mix thoroughly.
Pour the wet ingredients into the bowl with the dry ingredients and gently fold until just combined. Add the Snickers and gently combine.
In the bottom of a greased 13x9 inch glass pan, add ½ of the batter, pressing down until the bottom is covered. Drizzle with the caramel sauce, then add the rest of the batter to cover the caramel sauce.
Bake for 25-30 minutes, or until the top is golden brown. Cool completely before serving.