Add butter to the bowl of the food processor. Coarse chop using the on/off switch. Add water, egg yolk and salt. Process until just combined. Add flour and process until dough just starts to form a ball, about 4 seconds. Form into disc and wrap with plastic wrap. Refrigerate for 30 minutes. If desired, dough can be frozen until ready to use.

Roll out dough on a well-floured surface, to 1/8 inch thickness. Transfer to 9 inch diameter tart pan with a removable bottom. Ease dough into the pan edges with your fingers. Refrigerate for 30 minutes.

Heat oven to 400 degrees. Spread mustard over the prepared crust and top with shredded cheese.

Arrange tomato slices, overlapping each slice, to cover the tart’s surface. Bake the tart on a foil-lined sheet pan for 40-45 minutes, until edges are golden. When the tart is done, remove it from the oven, sprinkle with coarse kosher salt and finish with a drizzle of basil-infused olive oil and fresh basil. Allow it to cool for 10 minutes before removing it from the tart pan. Serve warm or at room temperature.