Cover a medium baking sheet with parchment and place it near the stove. The lined surface should be ready to receive the candy without any last-minute preparation.
Add the butter, granulated sugar, vanilla, and salt to a heavy-bottomed saucepan, then set the burner to medium. As the butter liquefies, the mixture will look pale and buttery.
Allow the sugar to dissolve, then maintain a simmer while whisking continuously until the candy reaches 285°F, generally 15 to 20 minutes. The mixture should deepen to dark amber, with the whisk keeping the butter and sugar together.
Transfer the hot candy onto the lined sheet and leave it undisturbed for 20 minutes. The poured mixture should harden into a firm sheet before you coat it.
Melt the milk chocolate gently, distribute it across the hardened candy with a spatula in a thin, even layer, and scatter both toasted nuts over it while wet. The glossy coating should cover the surface, with nuts resting in the chocolate rather than on a dry layer.
Chill for about 1 hour until the chocolate sets, then remove the candy, break it into pieces, and transfer it to an airtight container at room temperature. The topping should feel firm, while extended refrigerator storage can leave the candy damp and less crisp.