In a cast iron skillet, melt the butter. Use medium heat. For extra flavor, leave the butter on medium heat while stirring until the solids collect in little bits at the bottom and the butter is no longer foamy. This brown butter really brings out the nutty profile of the butter and will make your cream of condensed soup even more delicious.

Now that your butter is browned or melted, add your diced onion into the skillet. Stir them occasionally so they don't stick to the pan. Allow the onions to cook until translucent. I prefer to take the time to caramelize the onions, but that step is not necessary if you're in a hurry.

Once your onions are cooked to your liking, add in your flour and stir it until it's fully absorbed by the butter. This roux will be very thick and stiff. If all of your flour doesn't absorb, add a little bit of butter at a time until all of the flour is wet.

Next, spread this roux onto the bottom of your skillet so it can cook the flour. Stir every now and then so it doesn't burn. I usually cook this roux for 2-3 minutes.

Finally, add in your milk a bit at a time. With each addition of milk, stir the milk in fully until he mixture is consistent throughout. Then you can add more milk. Remember, this recipe is meant to replace a condensed soup, so it should be very thick when you're done.

Scoop it up into a half pint jar or go ahead and use it in a recipe.