½ pint butter pecan ice cream, softened at room temperature until pliable
Line a 9×5″ loaf pan with plastic wrap, leaving a few inches of overhang on all sides. Chill pan until ready to use. Toast pecans in a dry small skillet over medium heat, tossing occasionally, until fragrant and slightly darkened, 5–8 minutes. Let cool, then coarsely chop; set aside.
Using an electric mixer on medium-high speed, beat cream and powdered sugar in a large bowl until stiff peaks form, about 3 minutes. Place jam in a medium bowl and whisk to loosen, then gently mix in half of the whipped cream. Mix vanilla and salt into plain whipped cream.
Scoop half of vanilla whipped cream into prepared loaf pan and spread into an even layer. Arrange a layer of crackers on top, breaking or cutting to fit as needed. Add half of peach whipped cream, smooth into an even layer, and top with another layer of crackers. Dollop ice cream across top and smooth into an even layer. Add a third layer of crackers, followed by remaining peach whipped cream. Repeat with a fourth layer of crackers and finally spread remaining vanilla whipped cream over (don’t worry if it’s a little higher than edges of pan). Scatter reserved pecans on top. Cover with plastic overhang and freeze until set, at least 6 hours.
To serve, using plastic overhang, unmold cake (if it’s hesitant to come out, run the sides of the pan under warm water for a few seconds to loosen) and cut into slices.
Do ahead: Cake can be made 2 days ahead. Keep frozen.