Special equipment: a 2-inch round biscuit cutter
Make the biscuits: Preheat the oven to 375 degrees F. Prick the surface of the potato with a fork, put the potato on a baking sheet and roast until it is soft and a paring knife easily slips into the center, about 1 hour. Cool briefly, then halve and scoop the flesh out from the skin (discard the skin) and into a small bowl. Mash the potato until smooth, then refrigerate until cold, at least 1 hour.
Increase the oven temperature to 425 degrees F. Line a baking sheet with parchment paper and set aside.
Whisk together the cold potato puree and the muscovado sugar in a medium bowl until smooth. Whisk in the buttermilk.
Whisk together the 2 1/4 cups flour, baking powder, baking soda and salt in a large bowl. Sprinkle the cubed butter over the dry ingredients, and using your hands or a pastry blender, cut the butter into the flour until the mixture resembles very coarse cornmeal with the largest pieces of butter about the size of a large pea. Stir in the sweet potato mixture and gently mix until a soft dough forms.
Turn the dough out onto a floured work surface and pat it into a 1-inch-thick round. Using a 2-inch round biscuit cutter, stamp out as many biscuits as you can. Gently press the scraps together and stamp out more biscuits. Place the biscuits about 1 inch apart on the prepared baking sheet, then brush the tops with the cream and bake until golden brown, about 15 minutes. Remove from the oven and brush with the melted butter. Transfer to a bowl or basket and loosely cover with a kitchen towel to keep warm while you make the ham, gravy and eggs.
Make the ham steak and red-eye gravy: Heat the oil in a large cast-iron pan over medium heat. Add the ham steak and cook on both sides until golden brown, about 4 minutes per side. Transfer the ham to a cutting board.
Add the onion to the drippings in the pan and cook, stirring often, until slightly soft, about 1 minute. Add the brown sugar and some salt and pepper. Cook, stirring often for 1 minute. Stir in the flour and cook while stirring constantly for 1 minute. Slowly stir in the coffee, bring the gravy to a simmer, and cook, stirring, until thickened, 2 to 3 minutes. Stir in the butter, then remove from the heat, taste and season with more salt and pepper if needed. Cover to keep warm while you make the eggs.
Make the scrambled eggs: Beat the eggs until well combined in a large bowl. Season with some pepper. Melt the butter in a medium nonstick skillet over medium heat. Add the eggs and immediately start to stir with a wooden spoon or heatproof rubber spatula to form small curds. Once the eggs are barely set, add some salt and cook, stirring constantly, just until the eggs are set but still very soft and loose. Remove from the heat.
Cut the ham into large chunks and divide among 4 plates. Top the ham with a scoop of eggs, gravy and a few cilantro sprigs. Add 2 biscuits to each plate and serve immediately.