Preheat your oven to 350°F (175°C). Grease and flour two 8-inch round cake pans. Line the bottoms with parchment paper.
In a large bowl, whisk together the flour, cocoa powder, sugar, baking soda, baking powder, and salt.
In a separate medium bowl, mix the plant milk, vegetable oil, vanilla extract, and apple cider vinegar. Pour the wet ingredients into the dry ingredients and mix until just combined. Do not overmix.
Carefully stir in the hot water or coffee until the batter is smooth. The batter will be thin.
Divide the batter evenly between the prepared cake pans. Bake for 30 to 35 minutes, or until a toothpick inserted into the center comes out clean.
Let the cakes cool in the pans for 10 minutes before inverting them onto a wire rack to cool completely.
Prepare the raspberry filling: Combine raspberries, 2 tablespoons sugar, and cornstarch in a small saucepan. Heat over medium heat, stirring constantly, until the mixture thickens, about 5 to 7 minutes. Remove from heat and let it cool completely.
Prepare the chocolate frosting: In a large bowl, beat the softened vegan butter until creamy. Gradually add the powdered sugar and 1/2 cup cocoa powder, alternating with tablespoons of plant milk, beating until smooth and fluffy. Add more milk if needed to reach a spreadable consistency.
Once the cakes are completely cool, place one layer on a serving plate. Spread the cooled raspberry filling evenly over the first layer.
Top with the second cake layer. Frost the top and sides of the entire cake with the vegan chocolate frosting.
Notes
For an intense chocolate flavor, use high-quality Dutch-processed cocoa powder in both the cake and the frosting.
If you need a gluten free vegan chocolate raspberry cake option, substitute the all-purpose flour with a 1:1 gluten-free baking blend that contains xanthan gum.
For a bakery style vegan cake appearance, chill the assembled cake for 20 minutes before applying the final layer of frosting.