Ham and Cheese Puff-Pastry Bites with Honey Mustard

This recipe is from Barbara Lynch's STIR cookbook. The flaky puff pastry with melted gooey grueyere and salty ham is such a good combo and simple to make.  I have also found that this appetizer satsifies the most picky of palates.

For the honey mustard:
2 tablespoons extra virgin olive oil
1 large spanish onion, thinly sliced
3 tablespoons honey
3 tablespoons full-flavored Dijon mustard

For the ham and cheese bites:
2 sheets frozen puff pastry, preferably all-butter, thawed as the package directs
1/2 lb. thinly sliced ham
1/2 lb. thinly sliced (or grated) Gruyere
1 large egg, beaten
Fleur de sel

To make the honey mustard:
Heat oil in a skillet over low heat.  Add the onion and cook, stirring occasionally, until the onion is very tender (about 20 minutes).  Add the honey and mustard and cook, stirring occassionally, for another 5 minutes.  If the mixture begins to stick, you can add up to 1/4 cup water.  Let the mixture cool and then transfer to a food processor or blender and puree until smooth.  Season with salt and pepper.

Note:  the honey mustard will keep for up to a week, covered in the fridge.

To make the ham and cheese bites:
Heat the oven to 375 degrees F.  Line a baking sheet with parchment paper.  Roll the puff pastry to a thickness of about 1/8" (if necessary).  Lay one sheet of the puff pastry on the baking sheet.  Spread all of the honey mustard over the pastry, leaving a 3/4" border around the edge of the puff pastry sheet.  Lay all of the ham and then the cheese over the mustard, overlapping where necessary.  Brush the 3/4" border with some of the beaten egg and then place the other sheet of the puff pastry on top.  Seal the edges together by pressing down firmly around the edges.  Brush the top sheet with the remaining beaten egg and sprinkle with fleur de sel.  Lay a sheet of parchment paper over the top and then place the baking sheet over that to keep the puff pastry from puffing up too much during baking.

Bake for 20 minutes.  Remove top baking sheet and top parchment sheet.  Continue baking until the pastry is beatiful golden brown all over (another 10-20 minutes).  Let cool for at least 10 minutes before slicing into squares.