In a medium pan over low heat, add the olive oil and diced onion and stir. Add the sage and cook for 5 minutes, stirring occasionally. Add the maple syrup and vegetable broth.
Caramelize the onions by continuing to cook low and slow, stirring occasionally.
You can add more vegetable broth to keep it moist while you wait for the onions to brown and turn soft.
Once caramelized, set aside to cool slightly.
Once cool, add to a blender or food processor, with the mayonnaise, lemon juice, salt, pepper and jalapeño or cayenne if you’re using it. Blend until mostly smooth, with slight chunks.