In a 10-inch skillet, melt butter over medium-high heat. Add carrot, celery, and onion and stir for about 8-9 minutes to allow the vegetables to soften.
Sprinkle flour over vegetables and continue to stir for about 3-4 more minutes until your vegetables are a tan/caramel color.
Pour in beef broth and chicken broth and stir, removing any stuck bits from the bottom of the skillet. Add bay leaf and dried thyme.
Allow your gravy to simmer for 20-25 minutes, stirring occasionally. Your gravy should be thick enough to coat the back of a spoon. Remove any foam that appears around the side of the skillet with a spoon.
Use a strainer and drain the gravy. Discard the vegetables.
Season with salt and pepper to taste.
It’s so important to make sure you don’t let the gravy get too brown during the sauteing phase. A gravy that is too brown can taste extremely bitter and is quite hard to fix.
If you find that your butter is browning too quickly or burning, lower the heat to medium. Consistent stirring before you add the liquid is key to stopping it from burning.
You can try and fix a bitter gravy by adding a pinch of sugar. For best results, have everything prepared and ready before you start cooking the gravy to avoid a bitter gravy.
You can always choose to make gravy with pan drippings if you prefer. You would need the drippings from roasted meat.