Combine the blueberries, sugar, and 1 cup of water in a small saucepan over medium heat. Stir once or twice to help the sugar start to dissolve. Bring the mixture to a gentle simmer and let it cook for 5 minutes, pressing the blueberries gently against the side of the pan with a spoon so they break open and release their color.

Add the dried culinary lavender to the pan. Stir it in and let everything simmer together for exactly 3 more minutes. Do not go longer than 3 minutes or the lavender flavor will turn sharp and soapy. Remove the pan from the heat immediately.

Set a fine mesh strainer over a medium bowl or large measuring cup. Pour the hot blueberry mixture through the strainer, pressing the solids gently with the back of a spoon to get as much syrup out as possible. Discard the blueberry skins and lavender solids left in the strainer. Let the syrup cool to room temperature, about 20 minutes, before using.

Juice your lemons until you have 3/4 cup of fresh lemon juice. Strain out any seeds.

Pour the cooled blueberry lavender syrup into a large pitcher. Add the fresh lemon juice and stir well to combine. Pour in the 4 cups of cold water and stir again. Taste the lemonade. If you want it sweeter, stir in an extra tablespoon of sugar dissolved in a splash of warm water. If you want it more tart, add another squeeze of lemon.

Fill glasses with ice and pour the lemonade over the top. Add a lemon slice and a sprig of fresh mint if you like. Stir before pouring each glass since the syrup can settle to the bottom of the pitcher.