Make the Date Sponge:

1. Preheat oven to 350°F (180°C/Gas 4). Grease and line two 9″ sandwich tins.
2. In a saucepan, simmer dates and tea for 5 minutes; purée roughly if desired.
3. In a bowl, whisk eggs, light and dark muscovado sugars, and golden syrup until pale.
4. Slowly whisk in melted butter, date purée, and vanilla.
5. Sift in flour, mixed spice, bicarb, and salt; fold gently until just combined.
6. Divide batter between tins and bake 35–40 minutes, until a skewer comes out clean.

Prepare the Sticky Toffee Sauce:

1. In a saucepan off the heat, combine both sugars, butter, and golden syrup.
2. Warm gently to dissolve sugars, then bring to a rolling boil for 1 minute.
3. Remove from heat and stir in cream, vanilla, and salt. Set aside to cool.

Soak & Cool Cakes:

1. Poke holes in warm cakes with a skewer. Pour one-quarter of the sauce over each layer.
2. Reserve half the sauce for buttercream. Cool cakes completely in tins (2 hours+).

Whip the Toffee Buttercream:

1. Beat soft butter until creamy. Gradually add icing sugar, beating until light.
2. Stir in most of the reserved sauce (save a few Tbsp for drizzle). Add milk if too stiff.

Assemble:

1. Place one cake layer on a plate. Spread half the buttercream atop, then top with second layer.
2. Cover top with remaining buttercream. Drizzle with reserved sauce.