Preheat the Oven: Start by preheating your oven to 400°F (200°C).
Prepare the Pesto: In a food processor, combine the walnuts, garlic, a pinch of salt, and a handful of basil leaves. Pulse until finely chopped. Gradually add the olive oil while continuing to blend until smooth. Taste and adjust seasoning as needed.
Prepare the Puff Pastry: Roll out the thawed puff pastry on a lightly floured surface. Cut the pastry into squares (about 2 inches by 2 inches).
Assemble the Bites: Place a small cube of mozzarella and a cherry tomato half in the center of each pastry square. Add a dollop of the homemade walnut pesto on top.
Seal the Edges: Fold the corners of the pastry squares over the filling and pinch them to seal. Place the bites on a baking sheet lined with parchment paper.
Egg Wash: Brush the tops of the pastry with the egg wash to give them a beautiful golden color when baked.
Bake: Bake in the preheated oven for about 15-20 minutes or until golden and puffed.
Serve: Let cool slightly before serving and garnish with some extra basil if desired.