Preheat the oven to 350°F, and lightly grease two 8-inch round cake pans. Line the bottoms with parchment paper. You could also make it as a rectangular sheet cake in a 9×11 glass baking pan.

Measure the flour, cocoa powder, sugar, salt, baking soda, baking powder, salt and orange zest into a large mixing bowl.

Use a whisk or fork to mix the dry ingredients together, aiming to distribute everything as evenly as possible.

In a second bowl, lightly beat the eggs.

Add the yogourt and oil to the eggs as you continue beating.

Add the orange juice last, and immediately blend the dry and wet ingredients. It should end up as a fairly thick but smooth batter.

Boil the water, and stir in the instant coffee if you are using it.

Add it to the cake batter, stirring it in quickly. The batter will now seem somewhat thin - that's perfect.

Divide between the prepared cake pans and bake for 25 to 30 minutes. If you are using a rectangular glass pan, you'll want to bake for 30 to 35 minutes.

Let the cake(s) cool for at least an hour before you glaze.

Place the chocolate chips in a large bowl and set aside for now.

Place the orange zest and whipping cream in a saucepan at a medium-high temperature.

Bring to a simmer, removing it from the stove as soon as it begins to bubble.

Remove the orange peel from the cream as quickly as you can, and then pour the hot cream over the chocolate chips.

Make sure all the chips are covered, and place a lid over the bowl.

Let it sit for about 5 minutes, uncover, and swirl the chocolate with a whisk in a circular motion. The mixture should begin to get smooth and velvety in texture.

Once it's thoroughly mixed, let it rest for about 10 or 15 minutes at room temperature. It should be cool enough to spread with a spoon.

If you've made two round cakes, pour the glaze over the top of each first.

Place one cake on top of the other, and then use the back of a spoon to smooth the glaze over the sides.