01 -
Preheat the oven to 180°C (350°F). Grease a 23cm (9-inch) cake pan and line with parchment paper.
02 -
Combine 240ml milk with 1 tablespoon white vinegar. Stir and let sit for 5-10 minutes until curdled.
03 -
In a large bowl, whisk together the gluten-free flour, sugar, cocoa powder, baking soda, baking powder, and salt until thoroughly combined.
04 -
In a small bowl, mix cornstarch and water until thin and watery. Initially it will be thick but continue mixing until it loosens.
05 -
Make a well in the center of the dry ingredients. Add the cornstarch mixture, homemade buttermilk, warm water, vegetable oil, and vanilla extract. Whisk until smooth, switching to a spatula if the batter becomes too thick.
06 -
Transfer batter to the prepared cake pan and smooth the top with a knife. Bake in the center rack for 60 minutes, until the top is risen and slightly springy when touched, or a toothpick inserted comes out clean.
07 -
Allow the cake to cool in the pan for 15 minutes before removing to a wire cooling rack.
08 -
Use a cake knife to carefully cut a thin layer off the top to create a flat, level surface. Reserve the removed cake pieces for decoration.
09 -
Place chocolate chips in a heat-safe bowl. Heat heavy cream in a saucepan over medium heat, whisking constantly until it begins to simmer around the edges.
10 -
Immediately pour the hot cream over chocolate chips. Cover with plastic wrap for one minute, then remove and whisk until smooth and glossy.
11 -
Pour the warm ganache over the cake. Using an icing spatula, guide the ganache to drip down the sides of the cake.
12 -
Crumble the reserved cake trimmings and sprinkle around the top rim of the cake for decoration.