Preheat the oven to 350°F. Grease an 8 inch square pan, or line it with foil or parchment paper.
In a medium bowl, whisk together the flour, cocoa powder, salt, and espresso powder (if using).
Melt the butter and chocolate together in a double boiler or in the microwave. Once melted, transfer to a large bowl and whisk in the sugar until thoroughly mixed and shiny.
Add the eggs, vanilla, and pumpkin to the butter/chocolate/sugar mixture and whisk until very well-combined.
Fold the dry ingredients into the wet ingredients.
Pour the batter into your prepared pan and bake for about 40 minutes (start checking at 35 minutes). The brownies should pull away from the sides of the pan, and a cake tester inserted in the center should come out with a few moist crumbs clinging to it.
Let the brownies cool in the pan for at least 20 minutes before slicing and serving. They freeze very well!