In a small saucepan, combine the blackberries, water, lemon juice, zest and Swerve or sugar. Heat until it begins to boil.
Turn down the heat a little and mash the blackberries slightly to render the juice.
Turn off the heat and allow it to steep and cool completely. Store any leftover juice in the refrigerator.
Strain the berries and liquid in a fine mesh strainer into a bowl or large container, pressing the berries down to render as much juice as possible. Discard the solids left behind in the strainer.
In a shaker, combine the tequila, triple sec, juice of 2 limes, 4 oz. of blackberry juice and vanilla. Shake vigorously to mix.
Pour into pretty glasses filled with ice. Garnish with a slice of lime and a couple of blackberries. Cheers!!