Step 1

Heat the oven to 180C/fan 160C/gas Butter the base and sides of a straight-sided 20cm x 30cm tin.

Step 2

To make the base, use a wooden spoon to cream together the butter and sugar. Put the walnuts and 1/2 the flour in a food processor, and pulse until the walnuts are finely ground. Tip into the creamed butter with the cinnamon and the remaining flour, and mix to form a smooth dough. Weigh out 200g of the dough and knead in the baking powder and 2 tsp of water, wrap and set it aside.

Step 3

Press the remaining dough into the prepared tin to make an even base. Bake for 25 minutes or until golden brown, then cool for 1 hour.

Step 4

For the topping, put the condensed milk, honey and butter in a pan, and bring to a simmer, stirring constantly, until you have a smooth, light-caramel-coloured mixture. Stir in the salt, then spread evenly over the base

Step 5

Break up the reserved dough to make crumble-like chunks. Scatter them over the top of the caramel with the walnuts. Bake for 25 minutes or until the caramel is bubbling and dark brown around the edges. Cool completely, sprinkling over 1-2 pinches of sea salt, then cut into bars.