Step 1

Preheat your oven to 350°F. Grease or line a 9x13-inch baking pan and set it aside.

Step 2

In a large bowl, place the flour, xanthan gum, baking powder, baking soda, salt, spices, and granulated sugar and whisk to combine well.

Step 3

Add the brown sugar and mix to combine, breaking up any lumps.

Step 4

Add the melted butter, oil, beaten eggs, water, and vanilla, and mix to combine. The batter will be relatively thick, but soft.

Step 5

Scrape the batter into the prepared pan and spread it into an even layer with a moistened spatula. Shake the pan back and forth a bit to ensure even distribution of the batter.

Step 6

Place the cake in the center of the preheated oven and bake until set in the center, about 25 minutes. A toothpick should come out mostly clean (never wet; may have a few moist crumbs attached).

Step 7

Remove the pan from the oven and allow the cake to cool completely in the pan completely. It will take about 45 minutes at room temperature until completely cool.

Step 8

Once the cake is cool, dust the top of the cake with a thin layer of (the optional) confectioners’ sugar. Slice into squares and serve.