Salted Caramel Cake

Ingredients
Salted Caramel
300 g | 1 ½ cups granulated sugar
60 ml | ¼ cup water
1 tsp lemon juice
240 ml | 1 cup double (heavy) cream at room temperature
2 tbsp unsalted butter at room temperature
1 tsp sea salt or to taste
Chocolate Cake
200 g | 7oz dark chocolate chopped or chocolate buttons
200 g | 7oz (7/8 cup) unsalted butter cubed
125 ml | ½ cup hot coffee or water
75 ml | 5 tbsp buttermilk
3 large eggs
200 g | 7oz soft (1 cup) light brown sugar
200 g | 7oz (1 cup) caster sugar
200 g | 7oz (1 ½ cups) plain flour
25 g | 4 level tablespoons cocoa powder
1 tsp bicarbonate of soda
1 tsp baking powder
1/2 tsp salt
Salted Caramel Buttercream
180 ml (3/4 cup) pasteurised egg whites or from 6 eggs
500 g (6 cups) icing sugar
500 g (3 cups) unsalted butter at room temperature
1 tbsp vanilla extract or paste
1/4 tsp salt
3 tbsp salted caramel sauce (cooled)
Instructions
SALTED CARAMEL
Combine sugar, water and lemon juice to a deep heavy saucepan. Cook over high heat until the sugar dissolves, brushing the sides of the pan with a wet pastry brush to get rid of any sugar crystals.
Boil without stirring until the caramel turns a deep copper colour.
Remove from the heat, add the cream and quickly step back. The cream will cause the caramel to bubble volcanically before settling again.
Add the butter and use a small balloon whisk to stir until it melts.
Bring back to the boil, add the sea salt and cook until the thermometer registers 116°C (240°F),
Leave to cool slightly. Taste and adjust the salt if needed. Transfer to a clean jar and cool completely (in fridgbefore adding to buttercream.