Step 1

Preheat oven to 350 degrees and thoroughly grease a 9x13 pan.

Step 2

Mix the melted butter and sugars together in a large bowl until smooth. While continuing to mix, add the eggs and vanilla.

Step 3

Add the flour, baking powder, cream of tartar, and salt to the bowl of wet ingredients and stir until combined.

Step 4

Transfer batter to the prepared baking pan and press into an even layer.

Step 5

In a small bowl, combine sugar and cinnamon for the topping, then sprinkle over the batter.

Step 6

Bake for 20-25 minutes or until the top is just turning golden.

Step 7

Allow to cool for 30 minutes before slicing and serving.