Preheat oven to 400F. Line a baking sheet 10-15 inches with foil and arrange 28 crackers side by side. Form foil rims to prevent the caramel from dripping onto the baking sheet.
Combine butter, brown sugar, and salt in a saucepan. Melt, bring to a boil, and cook, stirring constantly for 3-5 minutes, until caramelized. Add vanilla and pour caramel over the crackers, covering them completely. Place in the oven for 5 minutes.
Melt the chocolate in a water bath or microwave.
Remove the baking sheet and wait 1 minute for the caramel to stop bubbling. Pour melted chocolate over the top and spread with a spatula. Let the crackers cool at room temperature, then refrigerate.
After cooling completely, peel off the foil and cut the caramel crackers into portions with a large knife. Store in a container with a lid in the refrigerator.