A layer of grapefruit slices and a grapefruity drizzle makes this zingy upside-down cake a wake-up call for the tastebuds. It's easy to whip up for an afternoon tea treat with a difference.

Combine the sugar, water, tarragon, and salt in a medium ... Strain the syrup through a mesh sieve into a medium bowl. Add the grapefruit juice to the syrup and whisk until completely mixed.