Position a rack in the lower third of the oven and preheat to 350ºF. Have the hot pie shell on a rimmed baking sheet lined with parchment for easy clean-up, and have a baking stone in the oven if you've got one.
Spread the pecan halves on a small baking sheet in a single layer and toast in the oven until fragrant and very slightly darkened in color, 10-12 minutes. To check if the pecans are thoroughly toasted, let one cool on the counter, then taste it – it should be crispy and have a toasty flavor. Let the nuts cool, then use your fingers to break each half into 4-8 pieces.
Reduce the oven temperature to 275º.
In a medium-large saucepan, melt the butter with the brown sugar and salt. Off the heat, gently whisk in the eggs one at a time, then the sorghum syrup, vanilla and 2 tablespoons of the bourbon. Return the pot to a low flame and cook, stirring constantly with a flexible heat-proof spatula, until the mixture is warm to the touch (130ºF on an instant-read thermometer). Remove from the heat and whisk in the remaining 2 tablespoons of bourbon and the pecan pieces. Pour the mixture into the hot, pre-baked pie shell. (If the pie shell has cooled, return it to the 275º oven for 5 – 10 minutes to heat it up.)
Bake the pie at 275º until the custard is mostly set, 20-30 minutes. Ways to tell when the pie is done:
The pie wobbles slightly when you shake it from side to side, but doesn’t slosh wetly.
When you press down on the center of the pie with the back of a spoon, the custard feels softly set, like Jell-o.
The sides of the pie may be very slightly puffed, but they should not be so puffed that the pie cracks around the edges.
An instant-read thermometer inserted into the center registers 160-165ºF.
Whew! Take that pie out of the oven and let it cool to room temperature, around 3 hours; it is still cooking from residual heat. Sprinkle with the flaky salt. For the cleanest slices, chill the pie until firm (an hour or so), then cut slices and let them sit at room temperature, or place them in a low oven for just a minute or two until gently warmed (but not melted). Serve slices with whipped cream or whipped coconut cream.
I like this pie equally cold, at room temperature, or very slightly warm. It keeps well, refrigerated airtight, for up to several days.