Have ready a candy thermometer, wooden spoon, pastry brush and cup of hot water for brushing sugar crystals from the sides of the pan.
Butter generously an 8 or 9 inch metal baking pan and set aside. Do not use glass; the piping hot candy may break it.
Combine the heavy cream and espresso powder in a heavy 3-quart saucepan. Place the pan on medium-low heat and heat the mixture, stirring, until the coffee dissolves. Add both sugars, the corn syrup, butter and condensed milk.
Raise the heat to medium-high and cook the mixture, stirring, until the sugar is dissolved and the butter is melted, about 5 minutes.
Bring the syrup to a boil, cover the pan and cook the syrup for 3 minutes. Remove the lid. Dip the brush in water and brush the sides of the pan. Attach the thermometer inside the pan.
Cook the syrup, without stirring, swirling the pan by the handle to cook evenly, until the candy reaches 240 to 245 degrees, frequently brushing the sides of the pan with the damp brush. This should take 13 to 14 minutes.
Remove the thermometer. Add the vanilla extract and swirl the pan to combine with the syrup.
Immediately pour the candy into the baking pan. Smooth evenly with the wooden spoon on a metal spatula. Set the pan on a wire rack to cool for 25 to 30 minutes.
Using a sharp knife, mark the top of the cooled candy into 1-inch squares for easier cutting. The candy will still be warm.
If candy is still not firm, let cool for a few more minutes. Then turn the candy out onto a chopping board, top side up. Using a large, sharp, buttered knife, carefully cut into 1-inch pieces, using marking on top as guide.
Spread the candy pieces on a sheet of buttered foil or wax paper and cool completely on wire racks.
For storing, wrap each piece in a square of wax paper or candy wrappers, or place between layers of wax paper in an airtight container.