Use ripe but firm peaches so they hold their shape. Frozen peaches work—thaw and pat dry before using. Store covered in the refrigerator for up to 4 days; the bars also freeze well for up to 2 months. For a hint of nuttiness, swap 1/4 cup of the flour in the crumble for finely ground almonds. A touch of almond extract in the cream layer pairs nicely with peaches.