Heat oven to 375°F. Line cookie sheet with parchment paper; set aside. Cut guava paste into thin slices (about ¼”-½” thick). Cut slices into 2”-long rectangles (you should have 6 rectangles); set aside. In medium mixing bowl, using spatula, stir together cream cheese and confectioners’ sugar until well combined; set aside.
Transfer frozen puff pastry dough to cutting board, keeping rounds of dough stacked. Using sharp knife, cut off rounded edges to form square shape. Peel off plastic wrap from each layer. Using rolling pin, roll dough squares, one at a time, until ½” larger all around.
Place square of dough on work surface. Add 1 piece guava paste and heaping tablespoon of cream cheese mixture. Using pastry brush, brush edges of dough with egg wash. Place second dough square on top of guava and cheese; gently press edges to seal. Brush top of dough with egg wash. Using small sharp knife, make 3 shallow cuts (about 1” long) on top of dough. Sprinkle dough with 1 tsp. sugar, if desired. Transfer pastry to prepared pan. Repeat with remaining ingredients. Transfer pan to refrigerator until dough is chilled.
Bake pastries until golden brown and puffed, 22-25 minutes. Transfer pastries to cooling rack; cool to room temperature; dust with confectioners’ sugar, if desired.