You can make foods fattier by saucing them. My favorite sauces of all time are aioli (garlic mayonnaise, sometimes with additional flavors like cumin), pesto, romesco, chermoula, and chimichurri. My mouth waters at the thought. These can all keep in the refrigerator for maybe a week.

Flavored Mayonnaise Variations - LA Times

Flavored Mayonnaise - Good Housekeeping

Sixteen Flavored Mayonnaise Variations - Luna Cafe

Wolfgang Puck's Pesto - no cheese! yay!

Romesco Sauce, Bon Apetit - without bread

Wolfgang Puck's Romesco Sauce - another without bread

Chermoula - Chicago Tribune

Chermoula - NY Times

Chimichurri

Chimichurri