Grease a 8x8 inch glass baking dish. Puree the mixture with an immersion blender
or blend in a Vitamix or similar until smooth. Pour the hot mixture into the greased baking dish and smooth the top. Let it cool to room temperature, then cover with plastic wrap and refrigerate for 24-48 hours until firm. Invert the membrillo / quince paste onto a platter (you may need to gently pry it out with a knife).
Note: Some recipes call for placing the membrillo in an oven at low temp (125 degrees F) for 8+ hours to firm it up. This membrillo is already firm and perfectly sliceable. If you prefer it even firmer, proceed with dehydrating it.
Cover with plastic wrap and store in the fridge for up to 3 months or longer.
For longer storage membrillo can be frozen well-wrapped for up to a year.