Prepare the crust: Spray a 9-by-5-inch metal loaf pan with cooking spray and line with plastic wrap, leaving a 2-inch overhang on all sides; spray the plastic wrap. Finely grind the peanuts and graham crackers in a food processor. Add the melted butter and pulse until combined. Press the mixture into the bottom of the prepared pan and refrigerate.
Make the ice cream: Bring 2 inches of water to a simmer in a saucepan over medium heat. Fill a bowl with ice water. Whisk the egg yolks, 1/2 cup sugar, the banana puree, hazelnut liqueur and salt in a large metal bowl. Place the bowl over the pot of simmering water (do not let the bowl touch the water) and whisk until thickened, 8 to 10 minutes. Remove the bowl from the pot and put in the ice water to cool.
Beat the heavy cream and the remaining 1/4 cup sugar with a mixer until the cream just holds stiff peaks (do not overbeat). Gently fold the cream into the banana custard.
Heat the peanut butter in the microwave until soft, about 20 seconds; let cool slightly.
Drop spoonfuls of the peanut butter into the banana cream and fold until swirled.
Spread the mixture over the crust in the pan, cover with plastic wrap and freeze until firm, at least 9 hours. Lift out of the pan using the plastic wrap and cut into 1-inch slices.