Preheat the oven to 400 degrees F; line 2 baking sheets with parchment.
On a floured surface, carefully roll out the sheet of pastry into a 10-by-12-inch rectangle. Dock the pastry all over with the tines of a fork and then brush it with the melted butter. Sprinkle over the manchego and 1/2 cup of the Parmesan. Using the rolling pin, press the cheese into the pastry. Cut the pastry into rounds using a 1 1/2-inch round pastry cutter. Gently press 1 slice of jalapeno into the middle of each round. Transfer to the prepared baking sheets. Sprinkle over the remaining 1/2 cup Parmesan.
Bake until golden brown and puffed, 10 to 12 minutes. Allow to cool before serving.