If your pineapple upside-down cake is undercooked and has a pasty texture due to excess liquid from the pineapples, there are a few things you can try to salvage it:
Return it to the oven: If the cake is just slightly undercooked, you can place it back in the oven for a few more minutes. Keep a close eye on it to prevent overcooking. This method can help dry out the excess moisture and firm up the texture.
Slice and broil: Another option is to slice the undercooked cake into individual portions and place them under the broiler for a short time. This will help brown the top and create a firmer texture. Be cautious not to leave them under the broiler for too long to avoid burning.
Toast or grill slices: Cut the cake into slices and lightly toast them in a toaster oven or on a grill. This can help evaporate some of the excess moisture and add a pleasant caramelized flavor to the cake.
Transform it into a trifle: If the texture of the cake is beyond repair, consider turning it into a trifle. Crumble the cake into small pieces and layer it with whipped cream, custard, or pudding, along with some fresh fruits. The creamy layers will help mask the texture issues, and you'll end up with a delicious dessert.
Remember, the final result may not be exactly like a perfectly cooked pineapple upside-down cake, but these methods can help improve the texture and flavor.