Step 1: In a medium bowl, combine the softened cream cheese and softened unsalted butter. Use a fork or an electric mixer on low speed to beat them together until light and fluffy. Season with salt and black pepper to taste. If using fresh herbs, stir them in now.
Step 2: Wash the English cucumber. Using a mandoline slicer or a very sharp knife, slice the cucumber into rounds as thinly as possible (about 1/16-inch thick). Lay the cucumber slices out on a few layers of paper towels and gently pat them dry with another paper towel to remove excess moisture.
Step 3: Lay out your slices of bread on a clean work surface. Using a sharp serrated knife, carefully trim off all the crusts from each slice. Save the crusts for breadcrumbs or croutons if desired.
Step 4: Generously spread a thin, even layer of the cream cheese mixture onto one side of each bread slice, going from edge to edge. Arrange a single layer of the patted-dry cucumber slices neatly over half of the bread slices, slightly overlapping them if necessary. Place another bread slice (spread-side down) on top of the cucumber-covered slices, ensuring the spread faces the cucumbers.
Step 5: Gently press down on each assembled sandwich to help the layers adhere. Cover the sandwiches loosely with plastic wrap or a damp paper towel and refrigerate for at least 15-20 minutes. This chilling step helps the spread firm up and makes cutting much easier and cleaner.
Step 6: After chilling, take each sandwich and cut it into desired shapes. Traditionally, tea party sandwiches recipes are cut into four equal rectangles (finger sandwiches) or two triangles. For a fancier look, you can use small cookie cutters. Arrange the cut sandwiches on a platter, garnish with a sprig of fresh dill or chives if desired, and serve immediately. If not serving immediately, keep them covered with a damp paper towel and plastic wrap in the refrigerator to prevent drying out.