Don't rush the caramel. Wait for the deep penny color and the faint bitter smell underneath the sweetness. If it seizes, pour the smooth caramel off the top and leave the grainy bits behind. Chill the cake for 10 minutes after each caramel layer during assembly. Store the finished cake in the fridge for up to 3 days; bring it to room temperature for an hour before slicing. You can freeze the layers separately for up to 3 months or the assembled cake for up to 2 months, but hold the top caramel drizzle until after thawing. For a nut-free version, swap the peanuts for crushed toffee bits.