In a food processor (I used my blender), blend the mayonnaise, onion and hot sauce. Add the shredded cheese and pulse until finely chopped. Add the pimientos and pulse until combined. Transfer the pimiento cheese to a bowl. Refrigerate until firm, at least 1 hour.
SERVE WITH: Crackers or vegetables
MAKE AHEAD: The pimiento cheese can be refrigerated for up to 3 days.