Preheat the oven to 400º F. Line one sheet pan with parchment paper. 

Once defrosted but still very cold, roll the dough out on a lightly floured surface, increasing the size of the pastry sheet by about ½ to 1-inch on all sides. 

Use a pastry cutter to cut the sheet of dough into four equal rectangles. Then use an offset spatula to smear about 1 teaspoon of Dijon mustard in the center of each rectangle. 

Sprinkle a little of the grated Gruyere cheese diagonally, on the dijon, then cover that cheese with the deli ham, about one slice of ham per danish.  Fold or crinkle the ham slice so it’s not a flat piece of ham. 

Sprinkle a little more cheese on top of the ham. Then place 3 to 4 peach slices on top of the cheese. 

Fold one corner of the pastry dough over the filling. Brush a little egg wash on the top of that folded-over corner. Then fold the opposite corner of the dough over the filling to meet and cover the egg-washed corner of the dough. Press lightly to seal. 

Brush the tops and sides of the danishes with the egg wash. Sprinkle poppy seeds over the tops. 

Bake the danishes for about 15-20 minutes, until the puff pastry is risen and golden brown. Rotate the tray halfway through the baking time to ensure even browning. 

Let the danishes cool for about 10 minutes then transfer to a serving plate and top with fresh basil leaves as garnish. Serve warm, cold, or at room temperature.