Preheat an oven to 180 C / Gas 4. Line two baking trays with foil. Place the matzo crackers in a single layer on the lined baking trays, breaking to fit, if necessary.
Bring the butter and brown sugar to the boil in a heavy bottomed saucepan over medium heat. Continue to cook, stirring constantly, until thick and smooth, about 3 minutes. Pour the hot caramel mixture over the matzo and spread evenly with a heat-proof spatula.
Place the caramel topped matzo in the preheated oven for 10 minutes. Remove from oven and evenly sprinkle chocolate chips on top. Return trays to oven to melt chocolate, about 1 minute. Smooth melted chocolate to completely cover the caramel. Sprinkle chopped walnuts over the melted chocolate. Chill in fridge for 20 minutes, or until set. Break into small pieces to serve.