Mix all the ingredients together in a bowl and set aside while you make the cake.
Line a baking tray with baking paper or a silicone mat.
Place the sugar and water in a saucepan and cook over a low heat, stirring until the sugar is dissolved, about 5 minutes.
Increase the heat, and stop stirring, the mixture will turn golden brown, watch it carefully.
Remove and add the sesame seeds
Pour onto the baking tray and allow to cool.
When cold break half the praline into shards, place the other half in a spice grinder or processor and grind. Alternatively pop in a ziplock bag and crush with a rolling pin.
Preheat oven to 180oC. Grease and line 2 round sandwich tins
Cream the butter and sugars together until light and fluffy.
Add the eggs one at a time, beating well after each addition.
Fold in the flour, baking powder, mixed spice, and pecan meal. Use a wooden spoon, and do not over mix.
Stir in the sour cream or yoghurt.
Divide the mixture in two and spoon into the prepared tins.
Sprinkle over the pecan nut and chocolate mixture.
Bake in preheated oven for 25-30 minutes until a skewer inserted in the centre comes out clean.
remove from the oven and place on a cake rack to cool
While the cake is baking make the buttercream icing.
Beat the butter in a large bowl until soft and light in colour.
Add half of the icing sugar and beat until smooth.
Add the remaining icing sugar and one tablespoon of the milk and beat the mixture until creamy and smooth.
Add remainder of the milk, if necessary, to loosen the mixture.
Swirl through the buttercream 1- 2 tablespoons of tahini
When cool remove cakes from tins.
Spread a few large dollops of icing across the top of one of the cakes.
Sprinkle with the crushed praline.
Layer second cake on top of first cake.
Spread with more buttercream, and drizzle with remaining tahini.
Decorate with sesame praline shards and serve