In a small sauce-pot on medium low heat mix the brown rice syrup and sugar. As the mixture starts to bubble around the edges, whisk so that the sugar dissolves. Do not let this mixture come to a boil. Remove from heat and add the butter, molasses, bourbon and vanilla. Whisk to mix. Set aside to cool to room temperature.
Preheat oven to 325F (163C). Toast the pecan halves for about 10-12 minutes until lightly toasted. They'll toast further as the pie bakes.
Arrange the pecans in the bottom of the pie, in an even layer with tops up.
Once the brown rice syrup mixture has come to room temperature, add the eggs and whisk until ingredients come together. Gently, pour the sugar-egg mixture over the pecans.
Bake for 45-50 minutes turning 1/2 way through baking. It's done when the center is just set but still slightly soft. If the crust starts to get dark, place a crust protector over the top of the pie or use foil to cover the edges.
Remove from the oven and allow to cool overnight so that the custard has time to set. Cover when completely cool and store at room temperature for up to three days.
Cutting this pie can be tricky because it has a soft set. Use a sharp knife and firm pressure when cutting. Dipping your knife in hot water and wiping it dry before cutting will help make a clean edge.
To reheat for service with ice cream, place in a 325F oven for about 8 minutes.