Heat oven to 350°F. For each flower cup, use 1 slice of white bread (thin-sliced is best). Trim crusts off bread, then cut each slice diagonally into quarters. Cut each quarter in half to make 8 small triangles.
Press 7 triangles around the sides of a mini-muffin cup. Press the 8th triangle into the bottom. Repeat with the rest of the muffin cups. Lightly coat bread with vegetable cooking spray, then bake for 10 minutes. Let cool.
Spoon some peanut butter into the center of each flower cup. Add a small spoonful of strawberry jam. Place peanut butter blossoms on plate with celery stalks.