Preheat the oven to 350°F (175°C). Grease and flour a 9-inch round cake pan.

In a mixing bowl, cream together the softened butter and sugar until light and fluffy.

Add the eggs, one at a time, beating well after each addition.

Mix in the buttermilk, orange juice, and orange zest until well combined.

In another bowl, whisk together the flour, baking powder, baking soda, and salt.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Pour the batter into the prepared cake pan and smooth the top.

Bake for 25-30 minutes or until a toothpick inserted into the center comes out clean.

Allow the cake to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.

In a mixing bowl, whip the cold heavy cream until soft peaks form.

Gradually add the powdered sugar, orange juice, and vanilla extract while continuing to whip until stiff peaks form.

Fold in the orange zest gently.

Once the cake is completely cooled, spread the frosting evenly over the top and sides of the cake.