Direction :

1. Make the dough: In a large bowl, whisk together the flour, sugar, yeast, salt, and nutmeg, if using. Add the currants, if using, and whisk to combine. Set aside.
2. In a medium bowl, whisk the egg with 1/2 cup of the milk. Set aside.
3. Melt butter in a small saucepan over medium heat. Add the remaining 1/2 cup of the milk and heat until warm to the touch, another 30 seconds or so. Whisk this milk-butter mixture into the bowl with the egg-milk mixture. Resulting mixture should be warm to the touch.
4.  Add the milk-egg-butter mixture to the bowl with the flour mixture. Use a spatula to combine all ingredients until flour is absorbed and dough is sticky. Sprinkle a handful of flour over the surface, and use your hands to briefly knead dough in bowl just until it all comes together—use more flour as needed, but go light. Dough should be on the sticky side.
5. Let the dough rise: Cover bowl with plastic wrap or a bowl cover. Let dough rise in warm draft-free area until doubled in volume, about 2 to 3 hours. (See notes above for creating a warm place for your dough to rise.)
6. Portion and proof: Butter a 9- or 10-inch square or round baking pan. Turn dough out onto a lightly floured work surface. If dough is especially sticky, knead briefly with a little bit of flour. Divide into 16 pieces. If you want perfectly sized balls, each portion should weigh about 60 grams. Roll each piece into a small ball using flour as necessary — this is a very sticky dough! Place balls equally spaced into pan. Cover with plastic wrap or a cloth bowl cover and stick in fridge overnight; or, if baking immediately, let rise again until rolls have doubled and are squishing against each other, 30 to 60 minutes (or more depending on how cold your kitchen is).
7. Eggwash and bake: Preheat oven to 375ºF. If you are doing the refrigerator rise, remove the pan an hour (or two if possible) before baking. Ideally the buns should be puffed, filling the pan, and light to the touch but it’s fine if you don’t see much of a change — they will puff in the oven. Brush the rolls with the egg wash. Bake for about 25 minutes, or until the rolls are evenly golden brown.
8. Make the frosting: In a stand mixer, beat the cream cheese with the confectioners’ sugar until combined. Add 1 teaspoon vanilla and a pinch of sea salt. (Alternatively, if your cream cheese is very soft, you can mix this with a spatula as opposed to a stand mixer.) Taste, and adjust with more sugar and salt to taste. Transfer to a piping bag or small ziplock bag. 
9. Frost the buns: Remove the pan from the oven. Let buns cool for at least 15 minutes before frosting: Snip off a corner of the storage bag, if using, and pipe an X over each bun.  Serve immediately.