Add the room temperature butter, maple syrup, maple extract and salt to the bowl of a stand mixer fitted with paddle attachment. Cream together the butter with the syrup, extract and salt until creamy and well combined, about 2 - 3 more minutes on medium speed. Stop and scrape down sides of bowl as needed.
½ cup (113 g) unsalted butter, room temperature, 3 tablespoons (45 ml) maple syrup, ¼ teaspoon maple extract, ⅛ salt
Mix in the sifted powdered sugar ½ cup (60 g) at a time along with 1 tablespoon (15 ml) milk or heavy cream, mixing in each addition of powdered sugar until incorporated. Scrape down sides of mixing bowl as needed.
3 cups (360 g) powdered sugar, 1 tablespoon (15 ml) room temperature milk or heavy cream, as needed
Once all the sugar has been added, mix on high until the maple buttercream is fully incorporated and your desired consistency. If the frosting is too thick, add 1 - 2 tablespoon (15 - 30 ml) more milk of choice or heavy cream, creaming until well incorporated.
Transfer the maple frosting to an airtight container or use to top your favorite cake, cupcakes, cookies or brownies.