Spray a baking pan with a nonstick cooking spray and place on a wire rack next to the stove.
Stir the sugar, honey, butter, cream of tartar, salt, and ½ cup water in a large saucepan over medium heat until the sugar has melted. Brush the sides of the pan with a moistened pastry brush to wash down any sugar crystals. Insert a candy thermometer into the pan and cook the syrup over medium heat without stirring until it starts to brown around the edges. Continue simmering, carefully swirling the pan occasionally, until the temperature registers 305° F.
Remove the syrup from the heat and quickly and carefully whisk in the baking soda. stirring just to incorporate it. (Watch yourself: the mixture will foam up!) Immediately pour the mixture over the surface of the prepared baking sheet. To keep the bubbles intact, do not touch the pan or try to spread the mixture out. Let cool until the top hardens, then sprinkle with the sea salt. Cool completely and break into large shards.
Storage tip: The honeycomb will keep in an airtight container at room temperature in cool, dry weather for up to 2 weeks.