Cucumber Dill Tea Sandwiches

loaf of square topped, thin white bread

Unsalted butter, softened at room temperature, optional

large or 2 medium cucumbers , peeled, seeded, grated, squeezed and patted dry

( 8 ounce ) cream cheese , softened at room temperature

grated Vidalia onion

mayonnaise

Kosher salt and white pepper ,

chopped fresh dill , plus more for garnish