In a medium saucepan, heat the butter over medium-low heat until melted (or warm oil).
Add the gluten-free flour and whisk until smooth.
Over medium heat, cook until the mixture turns a light, golden sandy color, about 6 to 7 minutes.
Meanwhile, heat the milk in a separate pan (or Pyrex) until just about to boil.
Add the hot milk to the flour mixture 1 cup at a time, whisking continuously until very smooth.
Bring to a boil.
Cook 10 minutes, stirring constantly, then remove from heat.
Season with salt and nutmeg, and set aside until ready to use.
