FOR THE CAKE
1/3 c. cocoa powder (31 g.)
1 tsp. instant coffee or pure vanilla extract (optional)
3/4 c. boiling water
1/3 c. oil, such as grapeseed or canola, plus more for pan (80 g.)
1/2 c. granulated sugar (110 g.)
1/4 c. packed brown sugar (53 g.)
1 tbsp. white vinegar
1/2 tsp. kosher salt
1 1/4 c. oat flour (130 g.) or all-purpose flour (160 g.)
1 tsp. baking powder
3/4 tsp. baking soda
FOR THE ICING
Zest of 1 orange (optional)
1/4 c. cocoa powder
1/4 tsp. instant coffee (optional)
1/2 c. plus 1 tbsp. powdered sugar, divided (67 g.)
2 tbsp. orange juice or water
Step 1
Preheat oven to 350°. Grease an 8” square pan with oil, lining with parchment if desired.
Step 2
In a large bowl, whisk together cocoa, instant coffee or vanilla (if using), and boiling water until smooth. Let sit for 2 minutes, then stir in oil, sugars, vinegar, and salt until fully incorporated. Stir in flour, baking powder, and baking soda until completely smooth, then pour into prepared pan.
Step 3
Bake until a toothpick inserted into the center of the cake comes out with only a few crumbs, about 30 minutes.
Step 4
Meanwhile, make icing: In a small bowl, whisk together orange zest (if using), cocoa, instant coffee (if using), ½ cup powdered sugar, and juice or water until completely smooth. Set aside until ready to use, giving the mixture a stir before pouring.
Step 5
Let cake cool to room temperature. Dust top of cake with 1 tablespoon powdered sugar, then generously drizzle icing all over.