Cook the bacon until crisp. Dry them in a paper towel and roughly chop. Lightly spray two cookie sheets with cooking spray. Set aside.

Cream the butter and sugar until light and fluffy. Beat in egg whites until combined. Add in the pastry flour, dried thyme, and chopped pistachio. Work the mixture until it comes together. Fold the cling film so that the dough is completely covered. Lightly roll it until you get a log, about 5 cm in diameter. Chill them at least 2 hours or overnight until thoroughly firm.

Preheat the oven to 350 degrees F.

Remove from the fridge, and slice the log into cookies, about 5 mm thick. Place the cookies on the prepared trays and bake 15 minutes. Cool the cookies on wire racks.

Stir them in an airtight container for at least a week.