Preparation

• Preheat the oven to 350 degrees and line an 11-inch tart pan with a removable bottom with parchment paper.
• In the bowl of a stand mixer, cream together the butter and ¼ cup, 1 tablespoon and 1 teaspoon sugar on low speed, about 7 minutes. Add ¼ teaspoon salt and 1 teaspoon vanilla extract. Mix again, then add 1 egg yolk and mix thoroughly, about 1 minute. Add the flour and mix until combined, 1 minute. Form the dough into a disc, wrap in plastic and refrigerate 20 to 30 minutes.
• On a floured work surface, roll out the dough into a 14-inch round 1∕8-inch thick. Drape the dough over the rolling pin and transfer it to the tart pan. Press the dough into place and trim the edges. Refrigerate again until firm, about 15 minutes.
• Bake the tart shell 10 minutes, until lightly golden brown. Remove and let cool on a wire rack.
• For the filling: In a double boiler, melt 1 cup chocolate chips. Remove from heat and add the remaining 3 egg yolks, the heavy cream, the remaining 1 teaspoon vanilla and a pinch of kosher salt. Whisk until combined and set aside.
• In the bowl of a stand mixer, whip the egg whites and the remaining ¼ cup plus 2 tablespoons sugar on medium speed until peaks form, about 2 to 3 minutes. Fold one-third of the whipped egg whites into the chocolate mixture until incorporated. Gently fold in another one-third and incorporate, then repeat with the last of the egg whites.
• Pour the filling into the tart shell and sprinkle the top with the remaining ¼ cup chocolate chips and chopped pistachios. Bake 10 minutes, until the sides souffle and the center is set. Let cool to room temperature before serving. Serve with ice cream, caramel sauce or whipped cream.