Loz,
Here is the recipe I use for hard tack, it's really easy, and you don't have to watch a thermometer!!!
Microwave Hard Tack
1 cup granulated sugar
1/2 cup light corn syrup
1/2 tsp. flavoring oil
food coloring
Thoroughly mix sugar and light corn syrup in a 4-cup microwave-safe glass measure. Cover with plastic wrap. Microwave on high for 3 minutes and 10 seconds. Remove from microwave and carefully remove plastic wrap. Quickly stir the sugar mixture and then cover with a NEW sheet of plastic wrap. Microwave on high for 3 minutes and 10 seconds. Remove from microwave, carefully remove the plastic wrap and stil. Stir in coloring and then flavoring. Pour syrup quickly, but carefully, onto greased cookie sheet score to mark squares: break into pieces when cool, dust with powdered sugar to keep from sticking, if desired.
This won't make as much as your recipe, but I like to make several different flavors so it works for me.