Place the butter in a 4-cup Pyrex glass measuring cup.
Melt the butter in the microwave on high power for 50 - 60 seconds, or until the butter is fully melted.
Add the flour and whisk it into the butter until well combined.
Microwave the butter and flour mixture on high power for one minute. Whisk.
Repeat this process. Microwave for one minute and whisk, two more times, for a total of three minutes.
The roux will be a light blonde color and very smooth. Whisk it together with 2 cups of broth and seasonings to create a liquid that will thicken to a gravy in the slow cooker.