1. Combine the butter and olive oil in a saucepan over medium-low heat.
2. Once the butter has just melted, add the garlic and cook for 2 - 3 minutes, until the garlic is fragrant. 
3. Sprinkle the flour into the pan, and whisk to form a paste. 
4. Cook the flour mixture (called a roux) for another 2 - 3 minutes, until it turns a golden brown color. 
5. Gradually add the broth to the pan, whisking continuously to incorporate the liquid and break up any lumps. 
6. Increase the heat to medium-high, and continue whisking until the mixture comes to a boil (4 - 5  minutes).
7. You will notice that the sauce will start to thicken. Reduce the heat to low and stir in the tomato sauce and spices. 
8. Continue to simmer for about 10 - 15 minutes, stirring occasionally. The sauce should be thick and smooth.
9. Remove from the heat, taste, and adjust the seasonings. Season with salt and pepper to taste.

Use the sauce right away or store in an airtight container in the refrigerator for 3-4 days, or in the freezer for a few months. If the sauce separates (which can happen after freezing), simply heat it in the microwave and whisk well before using it.