Heat the olive oil in a large saucepan. Add the onion, mushrooms, peppers and garlic and cook over medium heat for 5 -8 minutes.  

Meanwhile combine flour, paprika, and salt in a small bowl. sprinkle mixture over vegetables and stir well until fragrant.  Whisk in tomato paste, then slowly pour in the broth while whisking constantly. 

Raise heat to medium-high and bring the mixture to a simmer, then reduce heat as necessary to maintain a gentle simmer. Cook, whisking often, for about 5 to 7 minutes, until the sauce has thickened a bit and a spoon encounters some resistance as you stir it. (The sauce will thicken some more as it cools.)

Remove from heat, then whisk in the vinegar and season to taste with a generous amount of freshly ground black pepper. Add more salt, if necessary (I usually add another pinch or two).  Puree mixture in a blender or with an immersion blender.  

Use immediately or store in air-tight container in fridge for use during the week or freeze in small portions in an ice cube tray.