Preheat the oven to 375°. Mix the brown sugar and flour together, then cut in the butter to form a fine crumb. Use a pastry cutter, but if you use your hand instead, we won’t tell.

In a separate bowl, measure out the molasses and stir in the egg. Do not be tempted to whip. That’ll cause your pie to raise... and then sink while cooling.

Now slowly stir the hopefully-not-too-hot water into the molasses-egg mixture. Don’t overstir: it’s the alkali of the baking soda reacting with the acidity of the molasses that causes the pie to rise. Place the uncooked pie shell on a pizza pan to catch and crumb or goo spillover. Pour the molasses mixture gently into the pie shell. Then working quickly, scatter the crumbs across the molasses base. Don’t dump by the handful; you’ll probably end up doing it in three layers. Put the the pie in the middle of the oven and bake for 20 minutes. Then turn the temperature down to 325° and bake for an additional 35 minutes. Remove to cool.

And then let rest it for 3-4 days before serving: the molasses mellows, losing some of its bitterness; the cake layer absorbs more of the molasses, lessening the difference between the two layers, and the flavors deepen. One tester, whose family members must have way more willpower than mine, said it’s best on the seventh or eighth day after baking.

Oh, what a bear this recipe has been. That’s why you hire a pastry chef, someone who has the experience to understand how a small temperature difference in the hot water dramatically affects whether the pie boils over, or how a single difference of a tablespoon of butter in the crumb affects the color of the top of the pie way more than the temperature the pie bakes at.