Sablé Aux Olives Noires

Hard-cook the egg in boiling water for 10 minutes. Cool it under running water. Shell the egg, slice it in half; remove and reserve the yolk.
Pit the olives. Pat them dry to remove their layer of oil and chop them coarsely.
In a food processor fitted with the plastic blade, add the ingredients in the following order: butter, oil, confectioners' sugar, sea salt, hard-cooked egg yolk, flour, cornstarch, and finally, chopped olives. Process briefly, then form the dough into a ball, cover in plastic wrap, and chill in the refrigerator for 2 hours.
Adjust oven racks to upper and lower middle positions and preheat a convection oven to 325u0b0F or a traditional oven to 350u0b0F.
Divide the dough into two equal pieces. Flour a work surface, and roll out each piece into a 3/8-inch-thick round. Wrap in a piece of plastic wrap and store in the refrigerator until needed. Line baking sheets with parchment paper. Using a 21/4-inch-diameter cookie cutter, cut the dough into rounds and place them as you do so on the lined baking sheets.
Place the baking sheets in the oven and bake for 18 minutes (if using a traditional oven, rotate the baking sheets back to front and top to bottom once during baking). Transfer the cookies to wire racks and cool completely before storing them in an airtight container.