Preheat the oven to 350°F. Place the frozen phyllo tarts on a rimmed baking sheet. Set aside.
In a microwave safe bowl, combine the butter, vanilla, brown sugar, corn syrup and chocolate chips. Heat on high in the microwave for 30 seconds. Remove and whisk until the mixture is smooth. Whisk in the egg yolk and bourbon until no streaks remain.
Measure approximately 1/2 teaspoon of the finely chopped pecans into each phyllo shell. Then spoon enough chocolate custard mix on top to just cover it, about half way. Do not overfill or they will overflow while baking. Top each with a pecan halve.
Bake, uncovered, for 10 minutes. Remove and allow to cool before adding any desired garnishes.
Top with chocolate, caramel or flaky salt, if desired.
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Notes
You can swap out dark corn syrup and white sugar, if needed.
Bourbon is optional.
Store at room temperature for up to 3 days.