Don't make this! I've now made it four times and it comes out different (and not always good) every time. I'll work on it and will take this note off when it's consistently good.
This recipe was entirely inspired by the contest Your Best Recipe with Honey. It's a riff on the traditional Southern Chess pie, with a chocolate shortbread layer to cut some of the sweetness. When it came out of the oven, I wasn't really sure about it. Some of the batter had leaked onto the cookie sheet (good thinking, to put a cookie sheet under the tart pan!). It wasn't perfectly smooth on the top. So I left it to cool and my husband and I went to a movie. When we came home I took it out of the pan, and.... I didn't think my husband would like it because the chocolate shortbread isn't very sweet. (The filling part is super sweet.) But we both couldn't stop eating it. (I ate so much I got a headache from the sugar. This is not like me.)
There's always the question of which cocoa powder to use. I made the base with natural cocoa powder and with dutch process. I liked them both, but I found the dutch process cocoa powder to make the shortbread a little drier (but prettier, because it's so dark).
Heat oven to 325. Butter or pan spray a 9" pie plate or tart pan. In a stand mixer fitted with a paddle attachment, mix together butter, confectioner's sugar, cocoa powder and salt on medium low speed for about 2 minutes. Drape a towel over the top so you don't get cocoa-sugar dust all over your kitchen. You want it to blend together without incorporating a lot of air. Add flour a little at a time and mix in pulses until it is just blended together and starting to gather into dough.
Place the dough in the prepared pan and press on it with your fingers or with a glass with a flat bottom until you have an even layer of dough in the bottom of the pan. (If it is too sticky to work with, put it into the freezer for about 5 minutes.)
Bake for about 15-17 minutes. It will be slightly under baked--soft and a little puffy and smell like a brownie. Remove from oven and let cool to room temperature. (You can refrigerate it to cool it more quickly if necessary.)
You can make the filling the same day, or make the chocolate layer ahead, and when it's completely cool, wrap it well in the tart pan and refrigerate it. If you're making the honey layer, keep the oven on and take the heavy cream and eggs out of the refrigerator so they can come to room temperature.
Honey Pie Filling
Start the filling when the shortbread crust has cooled. In a small bowl, whisk together the flour and salt. Set aside.
Using a stand mixer fitted with a paddle attachment, beat the eggs and egg yolks with the brown sugar on medium speed until caramel colored and well blended, 2-3 minutes. Pour the melted butter, honey, vanilla and cream into the bowl and mix well on medium low speed until thickened, 2-3 minutes. With the mixer on the lowest setting, stir in flour just until blended and no streaks of white appear. Finish stirring by hand as needed.
Place the cooled pie plate on a large cookie sheet (If you use a two part tart pan, some of the filling will leak through as it bakes, so definitely do this.) The mixture will be quite runny, so carefully pour it into the pie pan. (If there are any bits of unincorporated flour pour it through a fine mesh strainer to ensure a smooth filling.) The pan should be no more than three-quarters full. Spread filling gently into an even layer. Sprinkle flaky salt over the top if desired.
Bake at 325 for 45-50 minutes or until it has mostly solidified, but may be a little jiggly. Turn oven off and let the tart sit for 10 minutes in the oven before removing to a wire rack. Let cool and serve at room temperature or refrigerate and serve cold.