Step 1

Batter – Preheat oven to 350F. Line an 8-by-8-inch baking pan with aluminum foil, spray with cooking spray; set aside.

Step 2

In a large, microwave-safe bowl melt the butter, about 1 minute on high power.

Step 3

Wait momentarily before adding the egg so you don’t scramble it. Add the egg, sugars, vanilla, and whisk until smooth.

Step 4

Add the flour, cream of tartar, optional salt and stir until just combined, don’t overmix.

Step 5

Turn batter out into prepared pan, smoothing the top lightly with a spatula; set aside.

Step 6

For Sprinkling – In a bowl (same one used for the batter is okay), combine the sugar, cinnamon, and stir.

Step 7

Using a small spoon, evenly sprinkle cinnamon-sugar mixture over the prepared pan. Looks like a lot but it sinks down and soaks in while baking.

Step 8

Bake for about 24 to 25 minutes, or until done. A toothpick inserted in the center should come out clean, or with a few moist crumbs, but no batter. Place pan on top of a wire rack to cool for at least 15 minutes before slicing and serving. Bars will keep airtight at room temperature for up to 1 week, or in the freezer for up to 6 months.