I am embarrased to say I have been making 1 gallon all grain batches. As far as the simple syrup, I used a very light version which was approx. 1.0 cup fresh blackberry : .25 cup sugar. I combined both in pot and cooked on med/high heat, mashing the blackberry as the sugar disolved. I use a potato masher, but any good multi-use kitchen utensil will do the trick. Once the sugar is disolved (about 8 minutes) remove from heat and set aside until you are ready to add to your boil. I added mine at the end of the boil after the last of the hops, when taken off the heat.
Simple Syrup Note for Making Wives Happy: 3:2 ratio fresh squeezed lemon juice to sugar slow boil 8 minutes w/ 3-4 large rosemary sprigs, cooled and combined with 1:1 ratio syrup to vodka (peach infused recommended), shaken with ice and topped with carbonated water, makes one killer summer cocktail.