Beat softened cream cheese until smooth. Stir in mayonnaise, Dijon, Worcestershire, lemon juice, hot sauce, and smoked paprika. Fold in grated cheddar, chopped pimentos, and green onion. Season with salt and pepper.
Spread pimento cheese thickly on two slices of bread. Add tomato or bacon if using, then top with remaining bread slices.
Butter the outside of each sandwich and cook in a skillet over medium-low heat, about 3 minutes per side, until bread is golden and cheese is melted.
Let sandwiches rest 1 minute, slice on the diagonal, and serve warm.
Notes
Pimento cheese keeps in the fridge for up to 5 days in an airtight container.
Freshly grated cheese melts better than pre-shredded.
Try adding pepper jack for a spicier version or mixing in a little horseradish for bite.
To bake: arrange sandwiches on a baking sheet and bake at 400°F for 6–8 minutes until golden.