To make this recipe gluten free, replace the French bread with a sturdy certified gluten-free loaf that can absorb the custard without falling apart too quickly. Also confirm that the vanilla extract, bourbon, and any other packaged ingredients are labeled gluten free or free from cross-contact concerns, since some brands may vary. Because gluten-free bread can behave differently from traditional bread, monitor the soaking time and texture closely so the pudding does not become overly soft before baking.