Line a rimmed baking sheet with parchment paper to prevent sticking and have all ingredients measured and ready near the stovetop.

In a large saucepan over medium-high heat, melt the salted butter completely.

Stir in granulated sugar, light corn syrup, and water into the melted butter, stirring continuously for about 2 minutes until the sugar dissolves.

Insert a candy thermometer into the mixture and cook, stirring frequently, until the temperature reaches 300°F, which usually takes about 15 minutes.

Once the mixture hits 300°F, remove from heat and quickly stir in the baking soda to aerate the mixture.

Add the almond slices and salted peanuts, then swiftly pour the hot mixture onto the prepared baking sheet.

Using a spatula or back of a spoon, spread the brittle as evenly as possible before it hardens.

Allow the brittle to cool completely for about 30 minutes, then break into pieces and serve or store.