Set out the block of cream cheese to soften at room temperature.
Preheat the oven to 350 degrees F. For the crust, whisk the flour, salt and baking powder in a pie dish. Whisk the olive oil and milk in a measuring cup and add the liquid to the pie dish. Toss with a fork to blend.
When the dough is mixed, gather it together and press it evenly along the bottom and up the sides of the dish to form a crust. Crimp the edges along the inside with two fingers. Poke holes in the bottom of the crust with a fork. Bake the crust for 10 minutes, then set it aside.
While the crust is parbaking, peel and chop the onions. In a large skillet, melt the tablespoon of butter over medium-high heat. Add the onions and cook them until tender, stirring occasionally, for about five minutes. (Do not brown them.)
After the crust has baked for 10 minutes, spread the cooked onions evenly over the parbaked crust.
In a medium mixing bowl, beat the cream cheese and egg with a mixer until smooth. Add the milk, chives (if using) salt, and hot sauce. Beat for a few seconds more to mix. Pour the filling over the onions.
Bake at 350 for 40 minutes, or until the top is set and getting browned (start checking after 35 minutes.) Let the pie rest for 10 minutes before slicing.
Store leftovers in the refrigerator for up to five days. You also can freeze the onion pie for up to two months.
Adapted from Cooking Light magazine (Aug. 2002) Nutrition facts calculated using low-fat cream cheese and low-fat milk.