Preheat your oven to 350°F (175°C) and prepare the Pullman loaf pan with parchment paper.

In a small bowl, sift together the gluten-free flour, cornstarch, baking powder, baking soda, cocoa powder, spices, and kosher salt.

In a large bowl, whisk together the brown sugar, molasses, vanilla, and neutral oil until smooth.

Add the eggs one at a time, whisking until smooth after each addition.

Gradually add the dry ingredients to the wet mixture, followed by the hot water. Stir gently until combined.

Pour the batter into the prepared loaf pan and smooth the top.

Bake for 55 to 65 minutes, until a toothpick comes out clean or with a few moist crumbs.

Cool in the pan for 10 minutes, then transfer to a cooling rack.

While cooling, prepare the frosting by beating together butter, cream cheese, salt, and vanilla until fluffy. Gradually mix in powdered sugar.

Once cooled, frost the loaf generously and slice to serve.