½ cup pecan halves
½ cup butter
¼ cup light corn syrup
½ cup packed light brown sugar
1/8 teaspoon salt
1 teaspoon vanilla extract
2 ½ cups rolled oats
Preheat the oven to 350F. Line an 8- by 8-inch baking dish with parchment (no greasing needed), or line with generously greased foil and set aside.
Place pecans on a baking sheet and toast in the middle of the oven until they are 1 or 2 shades darker, 7 to 9 minutes, stirring once after 4 minutes. Watch carefully to prevent burning. Remove from the oven, pour into a small bowl and place nuts in the freezer to cool until they can be handled safely. Once they are cool, coarsely chop the pecans.
In a 2-quart saucepan over medium high heat, melt the butter while swirling the pan periodically. Adjust the heat to maintain gentle bubbling until foam turns a very light golden color and the liquid butter underneath begins to brown, 3 to 4 minutes. Continue to cook and swirl the pan until the liquid butter under the foam turns copper-colored, 2 to 3 minutes more. Remove the pan from the heat and stir in the corn syrup until dissolved. Stir in the brown sugar and salt and return to heat. Boil for 1 minute. Remove pan from heat again and stir in vanilla.
Add oats and pecans to the saucepan and stir to coat. Pour the mixture into the prepared baking dish and spread evenly. Place a small piece of parchment paper or oiled foil on top of oats and press down firmly with your hand to flatten, paying attention to sides and corners. Use care: the mixture is still quite hot. Bake in the middle of the oven until the edges turn light golden brown, 13 to 15 minutes.
Remove from the oven and place on a cooling rack for 15 minutes. Remove the whole bar from the pan by lifting the edges of the parchment paper and place it on a cutting board. While still warm, use a large chef’s knife to cut the bar into 16 squares. Cut each square diagonally into 2 triangles (1 3/4 x 1 3/4 x 2 1/2-inch) to make 32 pieces. Cool completely, then store in an airtight container.