In a medium bowl, beat together cream cheese, lemon zest, lemon juice, fennel seeds, and pepper with a mixer at high speed until combined and creamy. Beat in blue cheese crumbles at medium-high speed until incorporated. Stir in celery and almonds.
Spread an even layer of cheese mixture onto 6 bread slices. Stack bread slices in pairs, cheese sides up. Top each with a remaining plain bread slice, creating 3 triple-stack sandwiches. Using a serrated bread knife in a gentle sawing motion, trim and discard crusts from sandwiches. Cut each sandwich into 3 equal rectangles, creating 9 finger sandwiches. Cut each finger sandwich in half cross-wise, creating 18 tea sandwiches. Serve immediately, or cover with damp paper towels, place in a covered container, and refrigerate for a few hours. For best flavor, let come to room temperature before serving.
Just before serving, garnish each tea sandwich with a celery leaf, if desired.
Recipe by TeaTime Magazine at https://teatimemagazine.com/creamy-celery-blue-cheese-triple-stack-sandwiches/