Preheat your oven to 400 degrees, and generously grease an 8x8 inch metal cake pan. Set aside.
In a large bowl, whisk together the flour, cornmeal, baking powder, baking soda, and salt. In a small bowl, stir together the melted butter, oil, milk, eggs, maple syrup, and vanilla extract. Pour the wet ingredients into the dry, and mix together until just combined.
Pour into your prepared baking dish and bake for 20 minutes, or until golden brown and toothpick comes out clean.
In a small bowl, stir together the melted butter, maple syrup, and salt. As soon as the cornbread comes out of the oven, brush a generous amount of the maple butter all over the top while it's still hot. Pop the rest of the butter into the fridge to solidify, and spread it onto the warm cornbread to serve!