Bring 5 cups of water to a boil.
In a large bowl, combine fresh blackberries and granulated sugar. Use a fork or potato masher to crush the mixture into a thick, jam-like consistency.
Add the Earl Grey tea bags (or loose-leaf tea) to the blackberry mixture, and pour the boiling water over it.
Let the tea steep for 5 minutes if using black tea. If substituting with green or white tea, steep for slightly less time.
While the tea is steeping, place 5 cups of ice in a large pitcher.
After the tea has steeped, strain the blackberry tea concentrate through a fine mesh strainer or cheesecloth over the pitcher of ice. The ice will melt, diluting the concentrate and cooling the tea.
Store the iced blackberry tea in the refrigerator for up to 7 days.
When ready to serve, pour the chilled blackberry tea over ice in a large glass. Add a drizzle of half and half or up to a half glass of milk, stirring gently. Garnish with fresh blackberries if desired.