In a large bowl whisk flour, sugar, baking powder, salt and nutmeg until combined and fluffy.
Use a pastry cutter or two forks to cut the butter into the dry ingredients until crumbly with small bits of butter still visible
Measure eggnog and add egg yolk if using. Whisk to combine.
Drizzle the cream mixture over the dry ingredients and stir gently just until combined. Press the mixture into a ball.
On a floured board roll out the dough gently to about ⅓" thick. Using a large biscuit cutter (or drinking glass) cut dough into circles.
Transfer to a baking sheet and bake for 15-18 minutes until just turning brown. Move to a cooling rack and allow too cool completely.
Melt white chocolate in a double boiler or microwave. Beat in the 2 tablespoons of eggnog until incorporated. Drizzle over scones and sprinkle with additional nutmeg if desired.