Dock the top of the sweet potatoes a few times with a fork then bake at 375℉/190℃ for about an hour until soft and tender. When the potatoes are almost done in the oven, make the brown butter.
1 cup purple sweet potato
Over medium heat, add the unsalted butter into a saucepan and allow to melt and bubble. Stir occasionally, scraping the bottoms and sides, until you see that the milk solids on the bottom of the pan have started to become golden brown. It will also start to become incredibly fragrant and nutty. Pour the butter into a heat proof bowl and set aside.
½ cup + 2 tablespoons unsalted butter
Remove the potatoes from the oven and allow to cool until you are able to handle them. Scoop all flesh out of the skins mash with a fork, or puree in a food processor to get it super smooth. Pass through a fine mesh sieve to remove any fibrous pieces, if desired.
Reduce the oven temperature to 350℉/177℃.
Once the potatoes are ready, combine the sweet potatoes, brown butter, heavy cream, milk, brown sugar, eggs, cinnamon, nutmeg, ginger, salt and vanilla into a large bowl and whisk until completely combined.
½ cup + 2 tablespoons unsalted butter, ½ cup heavy whipping cream, ¼ cup whole milk, ¾ cup light brown sugar, 2 large eggs, ½ teaspoon ground cinnamon, ½ teaspoon ground nutmeg, ¼ teaspoon ground ginger, ¼ teaspoon kosher salt, 1 teaspoon vanilla paste or extract
Pour the mixture into the par-baked crust and smooth out the top. Bake for 40-50 minutes until the edges are set and puffy, but the center still has a slight jiggle. Lightly tent the pie with foil (or use a pie shield) if the crust is browning too quickly.
Remove the pie to a wire rack to cool for 2 hours, then place in the fridge for 2 more hours before making the meringue topping. Adding the meringue before it is completely cool will make it melt and ooze off.