How to Make It
Prepare the gelato: Combine strawberries, vinegar, and 2 tablespoons of the granulated sugar in a saucepan. Cook over medium-low, stirring occasionally, until berries are very soft, 20 minutes. Mash with a potato masher; cool completely, 30 minutes.
Combine half-and-half, heavy cream, powdered milk, salt, vanilla, remaining 5 tablespoons granulated sugar, and cooled strawberry mixture in a large bowl. Process with an immersion blender until sugar is dissolved and ingredients are dispersed throughout, about 2 minutes. Cover and refrigerate until well chilled, about 2 hours.
Pour strawberry mixture into frozen freezer bowl of a 1-quart electric ice cream maker, and proceed according to manufacturer’s instructions. Transfer to a freezer-safe container; cover and freeze until firm, about 4 hours.
Prepare the Almond Shortbread: Place butter in the bowl of a heavy-duty stand mixer fitted with paddle attachment; beat on medium speed until fluffy, about 2 minutes. Add granulated sugar, salt, and almond extract; beat on low speed just until incorporated. Gradually add flour, beating on low speed just until blended after each addition. Shape dough into a 4 1/2-inch square about 1 inch thick. Wrap in plastic wrap, and chill until firm, 1 to 2 hours.
Preheat oven to 325°F. Position rack in upper third of oven. Line a baking sheet with parchment paper. Roll dough between 2 sheets of plastic wrap into a 6-inch square (about 1⁄2 inch thick). Remove plastic wrap; cut dough into 4 (3-inch) squares. Transfer squares to prepared baking sheet, leaving 2 inches of space between each. Bake until shortbread is light golden brown, 17 to 19 minutes. Cool on baking sheet 5 minutes; transfer to a wire rack to cool completely, about 20 minutes.
Prepare the Elderflower Crème: Beat all 3 ingredients on high speed with an electric mixer until stiff peaks form, about 1 minute. Serve gelato with shortbread; top with Elderflower Crème.