dark brown sugar, firmly packed
Place the white sugar, brown sugar, milk and corn syrup in a heavy about 3-quart saucepan over medium-high heat.
Stir to thoroughly dissolve.
Measuring the temperature with a candy thermometer, stir constantly with a long-handled wooden spoon.
When the mixture reaches "jelly" temperature on the thermometer (220 degrees), it will bubble furiously.
Splattering is a danger (this is why you want a spoon with a long handle).
You may wish to wear heavy rubber gloves for further protection. Continue stirring until mixture reaches 256 degrees ("medium-ball" stage).
Remove from heat, add vanilla and let it sit for 10 minutes.
During this time, set out the cupcake papers on the countertop and place 3-4 pecan halves in each paper.
Beat the mixture by hand with the wooden spoon, while it is still in the pan, until it loses its glossy sheen.
This can take up to 10 minutes or more, and calls for a strong arm.
At this point, the mixture will very quickly begin to form lumps and harden in the pan.
As this begins to happen, return the pan to low heat; add boiling hot water a tablespoon at a time, and beat out the lumps until nearly all are gone.
Add just enough water so that the mixture is somewhat runny and has lost much of its previous lumpy consistency (no more than about 3/4 cup of water, and often much less.)
Leaving a few lumps is permissible and often unavoidable.
Remove from heat and spoon it into the cupcake papers.
Let it harden for 20-30 minutes, then remove papers.
Be sure not to let the papers remain on after the candy has hardened somewhat or they will be difficult to remove later.
Store the pralines in an airtight container.