In a medium saucepan, bring butter, corn syrup, evaporated milk and sugar to a boil over medium heat, stirring constantly. Cook, stirring occasionally so the mixture doesn't scorch, until a candy thermometer reaches 236 degrees (it will take 8-10 minutes). Once it reaches 236 degrees, remove from heat and stir in vanilla and pecans. Continue to stir until very thick and dark in color, about 4-5 minutes (it will become somewhat difficult to stir...my arm was tired!) and immediately and quickly begin spooning onto wax paper or foil. Let sit until cool and completely firm.
Notes
Makes about 20.
Recipe by DessertedPlanet.com at https://dessertedplanet.com/pecan-pralines/