Flour and grease a 10-cup bundt pan. Set aside until needed.
Preheat the oven to 325 degrees F.
Add the butter and 4 ounces of chocolate to the top of a double boiler (or bowl set on top of a saucepan) over simmering water. Stir occasionally until the chocolate and butter has melted. Remove the pan from the heat and stir until smooth.
Add the cocoa and hot coffee to the butter mixture. Stir until smooth and well combined.
Add the granulated sugar and brown sugar and whisk to combine.
Add the oil and whisk to combine.
Add the eggs one at a time, whisking until combined. Scrape the sides and bottom of the bowl between each addition.
Add the Greek yogurt and vanilla to the mixture and whisk until incorporated.
Add the flour, baking powder, and salt to a large bowl and whisk to combine..
Slowly fold the flour mixture into the chocolate mixture just enough to combine. Don't overmix! It's okay to see a few specks of flour. Fold the remaining chopped chocolate into the batter.
Pour the batter into the prepared pan.
Place the bundt pan on the center rack of the preheated oven and bake for 1 hour 10 minutes or until a wooden skewer inserted in the center comes out clean or with a few moist crumbs,
Remove the pan from the oven and place it on a wire rack to cool in the pan for 10 minutes.
Invert the cake onto the wire rack and allow it to cool fully.