Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a large mixing bowl, combine the flour, granulated sugar, cocoa powder, baking soda, baking powder, and salt. Whisk until well mixed.
In another bowl, mix together the buttermilk, vegetable oil, vanilla extract, orange juice, and hot water. Stir until combined.
Gradually add the wet ingredients to the dry ingredients, mixing until just combined. Be careful not to overmix.
Divide the batter evenly between the prepared cake pans. Bake in the preheated oven for 30-35 minutes or until a toothpick inserted in the center comes out clean.
Allow the cakes to cool in the pans for about 10 minutes, then turn them out onto wire racks to cool completely.
While the cakes are cooling, prepare the frosting. In a large bowl, beat the softened butter until creamy. Gradually add the powdered sugar and beat until smooth.
Add the heavy cream, orange juice, orange zest, and vanilla extract to the frosting. Mix until well combined and fluffy.
Once the cakes are completely cool, spread frosting on top of one cake layer, then place the second layer on top. Spread frosting over the top and sides of the cake.
For the glaze, combine the fresh orange juice and granulated sugar in a small saucepan. Heat over medium heat until the sugar dissolves. Allow to cool slightly.
Drizzle the glaze over the frosted cake before serving.