• Preheat the oven to 170°C/Gas Mark 3.
• Grease a 25cm bundt tin and dust with cocoa powder, tapping out any excess.
• Melt the butter and allow it to cool slightly.
• Sift all the dry ingredients (plain flour, cornflour, milk powder, cocoa powder, baking powder, and salt) into a large mixing bowl.
• Sift again to ensure thorough mixing.
• Add the vegetable oil, whole milk, and melted butter to the dry ingredients, whisking until smooth.
• In a separate bowl, beat the eggs with the Kahlúa and vodka.
• Whisk this mixture into the batter until fully combined.
• Pour the batter into the prepared bundt tin and bake for 45–50 minutes, or until a skewer inserted into the center comes out clean.
• Allow the cake to cool in the tin for 25 minutes, then invert onto a wire rack and let it cool completely for 30 minutes.
• Meanwhile, wash and dry the bundt tin, as it will be used again for soaking the cake.

For the Syrup:

• In a pan, combine the butter, water, and caster sugar.
• Bring to a boil, stirring until the sugar dissolves.
• Reduce the heat and simmer until the mixture reduces by a third.
• Remove from heat and stir in the Kahlúa and vodka.
• Pour half of the syrup into the bundt tin, then carefully return the cooled cake to the tin.
• Let it soak for 5 minutes.
• Invert the cake onto a serving plate and brush the remaining syrup over the cake.

For the Cream Filling:

• Whisk the double cream, icing sugar, and chocolate hazelnut spread (or praline paste) together until medium peaks form.
• Spoon or pipe the cream into the center of the cake, or serve it separately.