Preparation

• Have ready a 10×15-inch rimmed baking sheet. If the sheet is not nonstick, lightly coat it with oil.
• Combine the sugar, corn syrup, butter, and 2/3 cup water in a heavy-duty 4-quart saucepan. Stir until all of the sugar is wet. Clip a candy thermometer onto the pan and cook the mixture over medium-high heat without stirring (it will be foamy) until it registers 310°F and is tan around the edges, 12 to 16 minutes.
• Remove from the heat and quickly remove the thermometer. Whisk in the baking soda (it will be foamy), and then the salt. Whisk in most of the seeds or nuts or all of the spice of your choice. Pour the mixture onto the baking sheet and tilt the sheet to spread it evenly. Sprinkle any remaining nuts or seeds on top. Cool completely on the baking sheet on a rack at room temperature, about 1-1/2 hours.
• Invert the brittle onto a large cutting board. Use a meat mallet, rolling pin, or your hands to break it up into medium-to-small pieces. The brittle can be stored in an airtight container at room temperature for up to 1 month.