First, roast your pecans. Preheat oven to 350° Fahrenheit. Spread whole, unsalted pecans on a cookie sheet and pop in the oven for 10-15 minutes until the nuts are a bit darker, dry, and smell fragrant (be careful not to let them burn!). Remove and let cool, then chop into small bits.

Then, brown the butter. In a small saucepan over medium-low heat, melt all of the butter and stir constantly until melted and simmering. Continue to simmer, on medium heat, for at least a few minutes, until the popping and hissing sounds have completely subsided (this is the water in the butter burning off - you'll know once it's silent). Continue to cook, stirring constantly, until the butter reaches a deep amber color and smells nutty or caramelly. Once it reaches that color, immediately take off the burner and let sit until cool. Once cool, pour into a small bowl and chill in the fridge until it's firm but not hard (essentially, the same softness as room temp butter).

Once your butter is firmed up to room-temp texture, make the cookies! In a large bowl, using an electric mixer, beat together the brown butter, white and brown sugars, and vanilla until lighter and fluffy. Toss in the flour, starch, and salt, and stir together using a spatula or wooden spoon until completely combined. Dump in the chopped, toasted pecans and stir to combine. The dough should be dry and stiff - if it seems too loose, add more flour. Separate the dough into two chunks and roll each one into a cylindrical or square log, about 2-inches in diameter (the slices of these logs will be your cookies, so make them the shape you want!). Wrap each log tightly with plastic wrap and let chill in the fridge for at least 2 hours or overnight.

Once the logs are chilled, preheat oven to 350° Fahrenheit and line two cookie sheets with parchment paper. Lightly grease the parchment paper and then unwrap the logs and slice 1/2 inch-thick cookies to place on the tray. They should not spread, so you can place the slices fairly close together. Bake for 17-20 minutes or until the edges are very lightly golden (they should not brown). Let cool completely before eating or serving (or they will fall apart).