Preheat oven to 350 degrees.

Line an 8x8 baking dish with parchment paper. (Alternatively, you can grease the baking dish and not use parchment paper.)

in a medium bowl, add the melted butter and brown sugar. Stir to combine.

Add the egg and vanilla. Stir to combine.

Add the flour and salt. Stir until fully combined.

Spread the batter in the prepared dish. The batter is thick, so just keep spreading until you have an even surface.

Combine the sugar and cinnamon. Sprinkle over the top of the batter.

Bake for 22 minutes or until a toothpick in the center comes out clean.

Allow to cool. Cut into squares.

Enjoy!