Over medium heat add butter and olive oil to a large sauté pan with sides.
Add the sliced garlic and sliced white or yellow onion. Let the onion and garlic cook until they begin to turn translucent but not brown.
Add the jar of roasted red peppers and the juice. You should use about 12 ounces or 1.5 cups of roasted red peppers and about 4 ounces or a ½ cup of the juice.
Add the can of diced tomatoes and the juice.
Season with salt, pepper, and some red pepper flakes. I like mine spicy, so I used a healthy pinch of pepper flakes. Stir well.
Simmer of medium/low heat for 10-15 minutes.
Once the sauce has had time to simmer, add the mixture into the food processor or blender. Blend until creamy and smooth, no lumps.
Pour the creamy sauce back into the sauté pan. Simmer over low heat until it reaches the thickness you desire. If it gets too thick, simply add a little of the reserved pasta water or veggie broth to thin it out.