Raspberry Puree
In a medium-sized saucepan over medium-high heat, bring the raspberries and sugar to a simmer. Cook, stirring constantly, until the fruit is soft and has fallen apart, about 5 to 10 minutes. Place a fine-mesh sieve over a bowl and press the fruit through the sieve with the back of a ladle. Discard the seeds. Stir in the vodka. Cover and refrigerate the puree until cold.

Ice Cream Base
Line a freezer-safe container or baking tin with plastic wrap or parchment. Set aside.

Measure 1 cup (250 mL) of fruit puree and set the rest aside to swirl in later.

In a large bowl combine the condensed milk, vanilla, salt, and 1 cup raspberry puree. Be sure to scrape all the condensed milk from the tin.

In a large bowl using electric beaters or a stand mixer fitted with a whisk, whip the cream until it holds stiff peaks, about 2 to 3 minutes.

Mix a generous scoop of whipped cream into the condensed milk mixture. Fold in the remainder of the whipped cream being careful to keep as much air in the mix as possible.

Assembly
Spoon a layer of ice cream base into the freezer container. Drizzle with some of the puree. Alternate layers of ice cream and puree. The ribbons of puree will appear when you scoop.

Place a piece of plastic wrap directly on the surface to prevent ice from forming. Freeze until firm, at least 6 hours, preferably overnight.

To serve, allow to soften at least 10 minutes before scooping, longer if frozen overnight. Alternatively, place the ice cream in the refrigerator to soften for up to 45 minutes. Return to the freezer immediately after scooping.