Line a rimmed baking sheet with parchment paper to prevent sticking. Measure all the ingredients and keep them ready near the stove, as you’ll need to work quickly once the candy reaches 300°F.

In a large saucepan, melt the butter over medium-high heat. Once fully melted, stir in the granulated sugar, light corn syrup, and water. Stir continuously until the sugar dissolves completely, which should take about 2 minutes.

Attach a candy thermometer to the saucepan and cook the mixture, stirring frequently, until it reaches 300°F. This process typically takes around 15 minutes.

As soon as the thermometer reads 300°F, mix in the baking soda, ensuring it is evenly incorporated. Quickly fold in the almond slices and salted peanuts, then carefully pour the mixture onto the prepared baking sheet.

Use a spatula, the back of a large spoon, or a knife to spread the brittle evenly across the baking sheet before it hardens. Allow the brittle to cool completely for about 30 minutes.

Once fully set, break the brittle into pieces and enjoy! Store any leftovers in an airtight container to maintain freshness.