Line a cookie sheet with parchment paper greased with small amount of vegetable oil.
In a heavy bottomed two quart pot, combine sugar, corn syrup, salt and water.
Over low heat, melt the butter and sugar while stirring constantly.
Attach a candy thermometer to the pan, and turn up the burner to medium-high.
Stir constantly as the mixture boils, bring the syrup to hard crack stage (300 F).
Once you've reached 300, turn off the heat and stir in the butter, baking soda and vanilla (the mixture will foam up).
As soon as the butter has melted, pour brittle onto the prepared cookie sheet.
Once the brittle has completely cooled and hardened, break it into small pieces and pulverize it in a food processor with the peanut powder until very fine.
Store in an airtight jar until ready to use.
Notes
Makes about 2 cups of topping which I divided into 5 tall spice jars for gifting.