Prep the pan: Line a rimmed baking sheet with parchment and a second layer of foil if needed. Arrange the saltines in a single layer, touching edge to edge.
Make the caramel: In a saucepan, melt the butter and brown sugar over medium heat. Stir until smooth, then bring to a gentle boil. Let it bubble for about 3 to 4 minutes.
Flavor the caramel: Remove from heat and stir in the vanilla extract. Pour the caramel over the crackers.
Bake: Place the pan in a 400°F oven for 5 minutes.
Add chocolate: Remove the pan and immediately sprinkle chocolate over the top. Wait 2 minutes, then spread into a smooth layer.
Top and chill: Add your favorite toppings and refrigerate for 1 to 2 hours until set.