Line two large baking sheets with parchment paper or silicone mats. Set aside.

Toast the pecans: Spread the pecan halves on a dry baking sheet and bake at 350°F (175°C) for 6-8 minutes, or until fragrant. Be careful not to burn them. Set aside to cool.

In a heavy-bottomed 3-quart saucepan, combine the light brown sugar, granulated sugar, heavy cream, corn syrup, and salt. Stir over medium heat until the sugar is dissolved.

Attach a candy thermometer to the side of the saucepan, ensuring the tip is submerged but not touching the bottom. Bring the mixture to a boil, stirring occasionally.

Continue to cook, without stirring, until the mixture reaches the soft-ball stage, 236°F to 240°F (113°C to 115°C). This can take 15-20 minutes. The mixture will bubble vigorously.

Once the target temperature is reached, immediately remove the saucepan from the heat. Add the butter pieces and vanilla extract, but do not stir them in yet. Let the mixture cool, undisturbed, for about 10 minutes, or until the thermometer reads around 150°F (65°C).

After cooling, begin stirring the mixture with a wooden spoon. Stir continuously and vigorously for 2-5 minutes. The mixture will start to thicken, become opaque, and lose its glossy sheen. This is the crucial step for a creamy texture.

As soon as you notice it thickening, quickly stir in the toasted pecans.

Working quickly before it sets, drop heaping tablespoons of the mixture onto the prepared parchment paper, forming 2- to 3-inch patties. Leave some space between them.

Let the pralines cool and set completely at room temperature, which should take about 30-60 minutes. They will firm up but remain creamy inside.