Turn your oven to it's lowest setting.  Something like 150 - 200 Fahrenheit

Place washed and dried individual leaves in a single layer on your baking sheet.  I normally wash the whole stems, let them dry for a few hours, then take the leaves off the stems.  Do not try to dry wet leaves. You will steam them not dry them.

When the leaves start getting crunchy, about 1 ½ to 2 hours, turn the oven off but keep the basil leaves in the oven.  Once the leaves are really crunchy and cool, place in a plastic bag and remove air from bag before closing.  Either use your fingers to crumble the dried basil leaves or use a rolling pin (or a water glass).  Once the dried basil is crumbled, place in a glass jar.

Store in a cool and dry place.