Preheat oven to 350°F Spread all the nuts on ungreased baking sheet and bake until toasted, about 10 minutes, stirring once. Let nuts cool completely.
Line a shallow rimmed 15 1/2" x 10" baking sheet with parchment paper and grease lightly with butter. In a small bowl, place butter, vanilla and baking soda (no need to blend); set aside.
In a heavy-bottomed saucepan over high heat, bring sugar, corn syrup and 1/3 cup water to a boil, uncovered. While sugar cooks, brush down the sides of the pan with cool water. Boil sugar over high heat until it turns a light amber colour, about 12 minutes. Remove from heat and quickly stir in butter, vanilla and baking soda with a wooden spoon (the baking soda will make it foamy). Stir in nuts until coated and spoon mixture onto prepared baking tray. Spread brittle as thinlly as possible with a greased rubber spatula, as thinly as possible. Let brittle cool completely at room temperature.
Melt chocolate chips in microwave on MEDIUM, stirring every 10 seconds, until melted. Crack brittle into desired serving pieces and dip halfway into melted chocolate and place back onto greased parchment-lined baking tray. Sprinkle lightly with sea salt and allow chocolate to set.