Add the mayonnaise, cream cheese, and grated onion to a food processor. Blend until smooth and well combined.
Add the grated cheddar cheese and chopped pimentos.
Pulse until everything is incorporated and the pimento cheese reaches your desired texture. Be careful not to over-process if you want a chunkier spread.
Season with salt and pepper to taste.
Transfer the pimento cheese to a serving plate or bowl.
Refrigerate for at least 30 minutes to allow the mixture to set before serving.
Serve chilled with crackers or your favorite dippers.
Notes
Find ingredients notes, dietary swaps, recipe variations, and more tips in the notes above.