1Preheat the oven to 350F. In a large bowl, beat the butter, oil and sugars for a minute, until well blended. Add the eggs and beat for two minutes, until pale and creamy.
2Meanwhile, stir together the cocoa and boiling water - it will make a thick paste. Beat it into the butter-sugar mixture. Add half the flour, the baking soda and salt, beating on low just until combined. Add the coffee and vanilla, then the rest of the flour, beating just until blended. Divide among paper-lined muffin tins and bake for 25 minutes, until the tops are springy to the touch. Tilt them on their sides to allow steam to escape and help them cool before frosting. To make the glossy chocolate glaze, heat the cream with the corn syrup, then stir in the chocolate and set aside for a few minutes, until it melts. Stir until smooth and use it to dip or drizzle the cupcakes.
3Makes about 1 1/2 dozen cupcakes.