Chocolate Caramel Walnut Bars

Ingredients

For the shortbread base

1½ cups (180 g) all-purpose flour
½ cup (100 g) packed light brown sugar
½ cup (113 g) unsalted butter, melted
¼ teaspoon salt

For the caramel layer

1 can (14 oz/397 g) sweetened condensed milk
½ cup (113 g) unsalted butter
½ cup (100 g) packed light brown sugar
2 tablespoons light corn syrup
¼ teaspoon salt
1 teaspoon vanilla extract

For the chocolate walnut topping

1½ cups (about 255 g) semisweet chocolate chips
1 tablespoon neutral oil
¾ cup (about 85 g) walnuts, roughly chopped

Instructions
Prepare the pan and oven. Preheat the oven to 350°F (175°C). Line an 8-inch square baking pan with parchment paper. Leave some parchment hanging over two sides so you can lift out the finished dessert. Lightly grease any exposed sides of the pan.
Make the base. In a medium bowl, stir together the flour, brown sugar, and salt. Pour in the melted butter and mix until all the flour is moistened. The mixture should look crumbly but hold together when squeezed.
Press and bake. Tip the mixture into the prepared pan. Press it into a firm, even layer, reaching all the corners. The flat bottom of a measuring cup makes this easier. Bake for 20–25 minutes, until the edges are lightly golden. Set the pan on a cooling rack while you prepare the caramel. Leave the oven on.
Start the caramel. Add the sweetened condensed milk, butter, brown sugar, corn syrup, and salt to a heavy-bottomed saucepan. Cook over medium-low heat, stirring constantly with a heatproof spatula. Scrape the bottom and sides of the pan as you stir so the milk and sugar do not burn.
Thicken the caramel. Once the butter has melted and the mixture begins to bubble gently, continue cooking for about 8–12 minutes. It should become thicker and deeper golden. When you pull the spatula across the bottom of the saucepan, it should leave a trail that closes slowly. Remove the pan from the heat and stir in the vanilla. Be careful: hot caramel can cause burns.
Set the caramel layer. Immediately pour the caramel over the baked base and spread it evenly. Return the pan to the oven for 8–10 minutes, until small bubbles appear across the surface. This short bake helps the layer set. Place the pan on a rack and let it cool for at least 45 minutes before adding the chocolate. The caramel can still be slightly warm, but it should no longer be hot.
Melt the chocolate. Put the chocolate chips and oil in a microwave-safe bowl. Heat in 20-second intervals, stirring after each one, until smooth. Stop heating as soon as the remaining small pieces melt when stirred. You can also melt them in a bowl over a saucepan of gently simmering water.
Add the topping. Pour the melted chocolate over the caramel and spread it to the edges. Scatter the chopped walnuts evenly over the top. Press them down very lightly so they stick to the chocolate without sinking into it.
Chill and slice. Refrigerate the pan for at least 2 hours, or until the chocolate and caramel are firm. Lift the slab out using the parchment overhang. Let it stand at room temperature for 10 minutes, then cut it into 16 squares with a sharp knife. Wipe the knife between cuts for neater edges.
Tips

Use sweetened condensed milk, not evaporated milk. They look similar in cans, but evaporated milk will not give this caramel the same sweetness or consistency.

Keep the heat moderate. Caramel made with condensed milk can catch on the bottom of the saucepan quickly. If you see dark flecks or notice a scorched smell, lower the heat immediately and keep stirring. A heavy saucepan makes this step easier because it distributes heat more evenly.

Press the base firmly. A loosely packed base may crumble when you lift or slice the bars. Give extra attention to the corners and edges, where the mixture is easiest to leave uneven.

Choose the chocolate you like. Semisweet chocolate balances the sweet caramel. Milk chocolate produces a sweeter bar similar to a candy bar. If you use dark chocolate, choose one you enjoy eating on its own because its flavor will stand out.

Chop the walnuts into small pieces. Smaller pieces stay attached more easily and make slicing simpler. For a deeper nutty flavor, toast the walnuts in a dry skillet for a few minutes, then cool them completely before sprinkling them over the chocolate.

Avoid slicing straight from the refrigerator. Very cold chocolate may crack under the knife. A brief rest at room temperature and a warm, dry knife will give you smoother squares.