Arrange the crackers in a single layer on a rimmed baking sheet so that the baking sheet is completely covered with a solid layer of crackers. Set aside.
In a medium saucepan, melt the butter with the brown sugar and vanilla. Bring to a gentle boil over medium heat and boil until it starts to thicken, 1 to 2 minutes. Immediately pour the mixture over the crackers in an even layer. Use an offset spatula to spread the mixture all over the crackers. Bake for 5 minutes. Sprinkle the almonds all over, then let cool completely.