Megan's Pecan Pralines

Line 2 large baking sheets with wax paper.
In a large heavy pot, stir together the sugar and 1 cup evaporated milk. Attach a candy thermometer to the pot and place it over moderately low heat. Cook, stirring occasionally—use a pastry brush dipped in cold water to wash down any sugar crystals clinging to the side of the pot—until the sugar is dissolved, 2 to 3 minutes. Raise the heat to moderate and cook the mixture, undisturbed, until the thermometer registers 238°F (soft-ball stage), 12 to 15 minutes. Remove the pan from the heat and let the mixture cool, undisturbed, until the thermometer registers 220°F, about 6 minutes.
Using a wooden spoon, stir in the vanilla and butter. Continue stirring until the mixture is creamy and thick, 1 to 2 minutes. Stir in the pecan pieces. Working quickly, use a wooden spoon to scoop up heaping tablespoons of the praline mixture and a small metal spoon to scrape the mixture onto the prepared baking sheets, leaving about 1 inch between pralines. If the mixture starts to crystallize and harden, add 1 to 2 tablespoons evaporated milk and place over low heat, stirring, until the mixture softens then continue dropping on prepared baking sheets. Let the pralines harden at room temperature. DO AHEAD: Pralines can be made ahead, wrapped individually in waxed paper, and stored in an airtight container in a cool place, up to 1 week.