Roast three large sweet potatoes at 450F until a knife comes out clean. Peel, mash, and measure three cups, the rest is extra you can freeze. Let the oven cool to 350F.
Using a food processor, blitz the chocolate crumbs, add the salted butter and the two tablespoons of brown sugar. Blitz until combined.
Line the metal tart tin with a removable bottom.
Bake until set (approximately five minutes).
Mix the sweet potatoes with the unsalted butter, white sugar, brown sugar, eggs, half and half, condensed milk, cinnamon and ground nutmeg.
Fill the tart tin to the top leaving three to four milimeters for the mixture to expand- it will settle again when it cools.
Bake until set and a knife comes out clean (approximately 50 minutes).
For the meringue, set the oven to 400F. In a standing mixer, using the whisk attachment beat the egg whites with the sugar on medium speed until they become thick stiff peaks. Coat the top of the pie, leaving ripples and peaks. Let brown in a 400F oven (approximately two minutes).