This elegant frozen treat is easy to make -- and sure to provide cool relief (and lots of smiles) on hot summer days.
Line an 8-by-4-inch loaf pan with two layers of plastic wrap, leaving a generous overhang.
In separate bowls, soften vanilla frozen yogurt and orange sorbet (see Cook's Note); spread layers evenly in pan, beginning and ending with yogurt. Freeze until firm, at least 6 hours or up to overnight.
Invert terrine onto a serving platter; remove plastic. Smooth sides with a metal spatula, if desired. Cover loosely with plastic; freeze until ready to serve (up to 3 days). Garnish top with pistachios, if desired.
To soften frozen yogurt and sorbet, cut into large chunks, and microwave in 10-second increments, stirring in between.