Heat oven to 350 degrees. Butter an 8-inch pan, line the bottom with a circle of waxed paper, cut to fit, and butter the paper. Dust the entire pan with cocoa powder and set aside.

Mix cocoa powder, flour, espresso powder, baking powder, and salt in a medium bowl; whisk to break up any lumps.

In the bowl of a mixer, cream the butter and sugar together. Add the eggs, one at a time and then beat in the vanilla, scraping sides as needed and mixing until smooth. Add half of the cocoa-flour mixture and stir on low, then all the yogurt, mixing well, then the rest of the flour mixture. Mix until all is combined (it will be thick).

Spread the batter into the prepared pan, building up the sides just a bit more than the center (to help it cook evenly).

Place chocolate in a medium glass or ceramic bowl (tip: using a large glass measuring cup with a handle will allow you to pour it more easily over the cake)

In a small saucepan, heat coffee and cream to a low simmer- just until bubbles start to appear around the edges.

Pour the hot cream-coffee over the chocolate and whisk until smooth. Allow to cool a bit to thicken (usually about 10 minutes).

Prep the cake for the ganache by placing it on a serving or cake plate, tearing pieces of waxed paper and layering them all around the bottom of the cake, pushing them slightly under the bottom edge of the cake (you want the ganache to pool on the paper and not go underneath).

When the ganache is ready, pour it over the cake, holding the bowl of ganache in the center and letting it flow over the sides. Use a spatula to gently help push it evenly, but don't go too much over the ganache in order to keep it shiny and smooth (tip: if too much pools on the sides, it was probably not thick enough - go ahead and spoon it back into the center, but don't spread - just let it absorb back in and it should smooth out),

Remove the pieces of waxed paper to reveal the perfectly even edge (yes!).

Decorate edges with chocolate shavings, if desired (chopped nuts are good, too).