Place the cream and sugar in a medium pot. Sprinkle in the gelatine and let stand 5 minutes. Place the pot over medium heat, stirring occasionally until the sugar and gelatine have dissolved into the cream. Stir in the lemon zest and extract. Divide and pour the cream into six, 6 ounce decorative glasses or bowls. Cool the panna cotta to room temperature. Individually wrap and refrigerate the panna cotta until set, about 4 hours or overnight. When ready to serve, divide and top each panna cotta with raspberries, garnish with a mint sprig, and serve.