Denise advises using a sugar thermometer or probe to make the caramel. They are also vegan. 

Method: 

• Preheat the oven to 160°C fan/180°C. Line a 22cm square tin so the baking paper comes up the sides.
• For the shortbread: put the flour, sugar and salt in a food processor. Add the margarine and vanilla and whizz to form breadcrumbs.
• Transfer to the tin, then use your hands to press into an even layer and chill for 30 minutes.
• Prick the base with a fork and bake for 30 minutes or until golden brown. Leave to cool.
• For the caramel: place the pecans on a tray, toast for about 10 minutes at 200°C. then roughly chop. Set aside. Put the sugar in the saucepan and cook without stirring until melted and caramelised. Take off the heat and add the cream slowly (it may spit). Stir in the butter and salt. Return to the heat and cook stirring until the caramel reaches 116°C on a sugar thermometer or probe. Immediately add the pecans and mix briefly.
• Pour over the shortbread, spread evenly with a spatula and set aside for 4 hours or overnight to cool.
• For the topping: melt the chocolate over a bowl of simmering water, then drizzle or pipe the chocolate over the caramel. Press the pretzels into the chocolate to finish. Leave to set before cutting into bars.

Fine more of Denise's recipes here