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Preheat the oven to 350°F. Lightly grease an 8” square pan.
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Weigh your flours; or measure by gently spooning into a cup, then sweeping off any excess.
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To make the topping: In a small bowl, whisk together the flours.
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In a separate bowl, whisk together the sugar, cocoa, salt, and espresso powder.
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Pour the melted butter over the sugar mixture and stir until smooth.
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Add the flours to the sugar mixture and gently stir to make a uniformly moist mixture. Set the topping aside.
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To make the cake: Whisk together the flours, cocoa, salt, baking powder, baking soda, and espresso powder. Set aside.
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In a large mixing bowl using either an electric mixer or a stand mixer, beat the butter, oil, sugar, and vanilla until smooth, about 3 to 5 minutes on medium speed.
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Add the eggs one at a time, beating well after each addition. Scrape the bottom and sides of the bowl as needed.
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Add one-third of the dry ingredients to the batter, beating gently to combine. Gently beat in half the sour cream. Mix in another third of the dry ingredients, then the remaining sour cream. Stir in the remaining dry ingredients. Scrape the sides and bottom of the bowl, then beat briefly until the batter is smooth and fully combined.
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Spread the batter into the prepared pan and sprinkle with the topping, gently pressing it into the batter.
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Bake the cake for 36 to 42 minutes or until a toothpick or paring knife inserted into the center comes out clean.
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Remove it from the oven and cool on a rack. Dust the top with confectioners’ sugar before serving the cake right from the pan, if desired.
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Storage information: Store the cake, covered, at room temperature for several days; freeze for longer storage.
