In a small saucepan, bring port and preserves to a boil over medium-high heat. Reduce heat to medium; cook, stirring occasionally, until mixture reduces to ¼ cup, 15 to 20 minutes. Strain mixture through a fine-mesh sieve, pressing out as much liquid as possible; discard solids. Let cool completely.

In the bowl of a stand mixer fitted with the paddle attachment, beat butter at medium speed until smooth and creamy, 1 to 2 minutes. Beat in vanilla and salt. With mixer on low speed, gradually add confectioners’ sugar until combined. Add 2 tablespoons (about 34 grams) cooled port mixture; beat at medium speed until fluffy and well combined, 1 to 2 minutes, stopping to scrape sides of bowl. Use immediately.