Also known as Sea Foam Candy, Honeycomb Candy and probably even more crazy names! Closely adapted from Michael Harlan Turkell, who adapted from Aaron Cozadd.
Place a silicone mat (or parchment paper) in the bottom of a rimmed cookie sheet. Set aside.
Combine everything but the baking soda in a deep, straight-sided pot, 3-4 qts. Place a heatproof brush with a small bowl of water, a whisk and a heatproof spatula within reach.
Place the pot over high heat and cover. Bring the mixture to a boil and let stay covered for 3-4 minutes. Then remove the cover and use the heatproof brush to lightly and quickly brush the sides of the pot with a little water to prevent crystals.
Attach a candy thermometer to the sides of the pot. Boil until the temperature reaches 290 F (145 C).
Carefully and quickly whisk the baking soda into the boiling mixture (I left it on the burner but lowered the heat a bit). You want to stir quickly enough that the baking soda is evenly dispersed, but then stop just as quickly because you do not want to break the wonderful bubbles that are forming (they will form the distinct texture of this candy). Making sure your baking soda is clump free will help with this.
Immediately after whisking pour the mixture out onto your prepared cookie sheet. Use the heatproof spatula to quickly scrape all of the candy out of the pot.
Quickly sprinkle your toppings over the setting candy. It is important to sprinkle the toppings before the candy sets too much so they will adhere.
Let cool for 45-60 minutes before breaking the candy into irregular pieces. Store in an airtight container--it will keep a long time.