Flaky pastry for a 10" tart or deep dish pie plate.
3 T butter
2 1/2 lb onions, thinly sliced
1/4 c unbleached all-purpose flour
1/2 t salt
1/8 t nutmeg
1 t ground mustard
2/3 c milk
3 eggs
1 c sour cream
2 c (8 oz) Swiss, Greyere or Emmenthaler cheese, grated (I use Jarlsberg Swiss.)
Salt to taste
Preheat oven to 350 degrees.
Melt butter in a 3-4-quart straight sided saute pan over medium heat.
Add onions and cook, covered, stirring often, until soft (10-15 min).
Uncover and continue cooking, stirring often, until lightly brown (12-15 min).
Stir in flour, salt, nutmeg and mustard.
Remove from heat and slowly stir in milk.
Return to heat and bring to a low boil, stirring, and continue to stir and simmer the sauce until thickened.
Beat eggs in a large bowl, then stir in sour cream and cheese.
Stir onion mixture into the egg-sour cream mixture; check seasoning for salt.
Pour into prepared pastry.
Bake on the bottom rack for 50-55 minutes or until crust is browned and filling is firm when gently shaken.
Let cool on a rack a few minutes before serving.
Serves 8.