Preheat the oven to 350°F (175°C) and grease a baking dish with the extra salted butter.

Combine the ingredients for the base: In a mixing bowl, mix the diced salted butter, chopped pistachio kernels, plain flour, cornflour, golden caster sugar, and malted milk powder until a dough forms.

Press the dough into the prepared baking dish evenly and bake for about 20-25 minutes, or until it’s golden brown and fragrant.

Melt the filling ingredients: In a saucepan, combine the salted butter, granulated sugar, evaporated milk, tahini, and vanilla extract. Heat gently until everything is melted and smooth.

Stir in the marshmallow fluff until it’s fully combined and silky.

Pour the marshmallow mixture over the baked crust and smooth out with a spatula.

Prepare the topping: In another saucepan, melt together the unsalted butter, golden caster sugar, golden syrup, and condensed milk over low heat until combined and glossy.

Add the flaky sea salt to the melted mixture and pour it over the marshmallow layer.

Melt the dark chocolate and drizzle it over the top of the slice in a decorative pattern.

Sprinkle with the roughly chopped pistachio kernels for an added crunch.

Cool the entire slice at room temperature before slicing into pieces.