Make, shape, and bake the gluten-free pie crust until nearly fully baked as directed.
Spread the pecan halves on a small baking sheet in a single layer and toast in a 350ºF oven until fragrant and very slightly darkened in color, 10-14 minutes.
Let the nuts cool, then use your fingers to break each half into 4-8 pieces.
Reduce the oven temperature to 275ºF.
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 maple syrup, vanilla, and 2 tablespoons of the bourbon.
Return the pot to a low flame and cook, stirring constantly with a heat-proof spatula, until the mixture is warm to the touch (130ºF on an instant-read thermometer).
Remove from the heat and stir in the remaining 2 tablespoons of bourbon and the pecan pieces.
Pour the mixture into the hot, pre-baked pie shell.
Bake the pie at 275º until the custard is mostly set, 25-40 minutes.
Let the pie cool to room temperature, around 3 hours.
Top with a few pinches of flaky salt, if desired.
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.
