Combine the sugar, light brown sugar, cream, milk, and butter in a saucepan and cook to 110°C/230°F while stirring constantly.
Add the pecans and salt and cook to 114°C/237°F while continuing to stir constantly.
Remove from the heat and add the vanilla extract. Allow to cool, undisturbed, to 100°C/212°F.
Using awooden spoon, stir vigorously until the mixture begins to look creamy, about 45 seconds.
Using a no. 50scoop, deposit the pralines on parchment paper. (If the mixture crystallizes too much in the pan, becoming too thick, warm briefly on direct heat while stirring to restore proper viscosity.)
Use as soon as possible after making. Pralines lose quality quickly in storage.
Chocolate Peanut Pralines
Omit the butter and instead add 50g/2oz of cocoa powder and 60g/2oz of peanut butter to the mixture. Replace the toasted pecans with toasted chopped peanuts.