Millionaire's Shortbread

Before you start

Millionaire's shortbread is a three-layer bar popular across the U.K.: buttery shortbread on the bottom, a soft caramel in the middle and a thin layer of chocolate on top. Each layer has its own failure point. The base must be baked fully crisp so it does not turn soggy under the caramel; the caramel must be cooked long enough to set firm but still sliceable; the chocolate must be thin enough to cut without shattering.

The caramel here uses sweetened condensed milk, butter and brown sugar, stirred constantly over gentle heat until it thickens and darkens a shade. It needs patience rather than a thermometer. Stop stirring for even a minute and it can catch on the bottom of the pan and scorch.

Ingredients

• Shortbread base250 g (2 cups, spooned and leveled) all-purpose flour
• 75 g (⅓ cup) granulated sugar
• ¼ tsp fine salt
• 175 g (¾ cup) unsalted butter — softened
• Caramel1 can (397 g / 14 oz) sweetened condensed milk
• 115 g (½ cup) unsalted butter
• 100 g (½ cup packed) light brown sugar
• 2 tbsp golden syrup or light corn syrup
• ½ tsp fine salt
• Topping200 g (7 oz) milk or dark chocolate — chopped
• 1 tsp neutral oil
• 30 g (1 oz) white chocolate — optional, for feathering

Method

1. Heat the oven to 175°C (350°F). Line the pan with parchment, leaving an overhang on two sides for lifting.
2. Mix the flour, sugar and salt, then work in the butter with a spoon or your fingers until the mixture clumps together. Press it evenly into the pan and prick all over with a fork.
3. Bake for 20 to 25 minutes, until golden all over and firm in the center. Cool completely in the pan.
4. Put the condensed milk, butter, brown sugar, syrup and salt in the saucepan over medium-low heat. Stir until the butter melts and the sugar dissolves.
5. Raise the heat slightly so the mixture bubbles gently, and stir constantly, scraping the bottom and corners, for 8 to 12 minutes. It is ready when it has thickened noticeably, turned a light fudge color and leaves a brief trail on the base of the pan when you drag the spatula through it.
6. Pour the caramel over the cooled base and spread it evenly. Cool for 15 minutes, then refrigerate for about 1½ hours, until firm to the touch.
7. Melt the chocolate with the oil in a heatproof bowl over barely simmering water or in short bursts in the microwave. Pour it over the caramel and tilt the pan to spread it thinly. Drizzle with melted white chocolate and drag a toothpick through it if you like.
8. Let the chocolate set at room temperature for about 30 minutes, until just firm. Lift the slab out and cut into 16 squares with a hot, dry knife, wiping it between cuts.

Tips for success

• Cut while the chocolate is set but not rock-hard. Chilled for hours, the top cracks away from the caramel when sliced.
• Use a heavy pan for the caramel. A thin pan creates hot spots that scorch the milk solids and leave dark flecks.
• A little oil in the chocolate keeps it softer so the layers stay together when you cut and bite.

Substitutions

Golden syrup

Light corn syrup works the same way. Honey adds its own flavor and browns faster, so stir with extra care.

Shortbread base

For a gluten-free base, use 250 g of a 1:1 gluten-free flour blend. The base will be a little more crumbly but holds once the caramel sets.

Milk chocolate

Dark chocolate gives a less sweet bar that balances the caramel. A mix of half milk and half dark is a popular middle ground.

Variations

Salted caramel version

Increase the salt in the caramel to ¾ tsp and sprinkle flaky sea salt over the chocolate before it sets.

Biscoff layer

Replace the chocolate topping with 200 g melted white chocolate swirled with 3 tbsp warmed spiced cookie butter.

Troubleshooting

Caramel is runny and oozes when cut

It was not cooked long enough. Cook until clearly thickened and a shade darker, and let it set fully in the fridge before adding chocolate.

Caramel is grainy or has dark specks

The sugar was not dissolved before boiling, or it caught on the bottom. Dissolve over low heat first, then stir constantly over medium-low.

Chocolate cracks off in sheets

The bars were cut cold from the fridge or the chocolate layer was too thick. Add oil to the chocolate, keep the layer thin and cut at cool room temperature.

Soggy base

The base was underbaked. Bake until golden all over and cool it fully before pouring on the caramel.

Storage

Store in an airtight container in a cool place for up to 1 week, or in the fridge for up to 2 weeks. Let refrigerated squares sit for 10 minutes before eating. They freeze for up to 3 months, wrapped individually.

Safety notes

The caramel is extremely hot while cooking and sticks to skin, so keep children back from the stove. Contains wheat, milk and soy (in most chocolate). Do not eat the raw base dough.