Put 2 raspberries in each compartment of 2 standard 16-cube ice cube trays. Fill the trays three-quarters of the way with cold water. Freeze until solid, at least 6 hours and up to overnight.
Meanwhile, combine the sugar and 2/3 cup water in a small saucepan. Bring to a boil over medium-high heat then reduce to a simmer and cook, stirring occasionally, until the sugar is dissolved, 3 to 5 minutes. Let the simple syrup cool completely, transfer to a container and refrigerate.
When ready to serve, whisk together the simple syrup and lemon juice in a large pitcher. Add the Moscato and stir to combine. Divide the ice cubes among 6 glasses and fill with the Moscato mixture. Garnish with the mint sprigs and lemon rounds.
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