2 1/4 teaspoons salt
2 1/2 cups milk
Preheat the oven to 350 degrees F (175 degrees C). Melt butter in a large bowl in the microwave. Pour melted butter into a glass 9x13 inch baking dish. In the bowl you melted the margarine, whisk together eggs and salt until well blended. Gradually whisk in milk. Pour egg mixture into the baking dish. Bake uncovered for 15 minutes, then stir, and bake an additional 10 to 15 minutes, or until eggs are set. Serve immediately.
I have successfully made this with casein-free margarine and almond milk to make it gfcf.
I have also made a half-batch, using 1/2 the amount of each ingredient and baking it in a 8 inch square baking dish.