Dry toast the pepitos in a skillet until they start to pop.
Line the bottom and the sides of an 8-in square glass pan with parchment. Butter the parchment on the sides of the pan. Evenly spread out the toasted pepitos on the bottom of the pan, on top of the parchment.
In a saucepan, combine heavy cream, pumpkin puree and spices. Get this mixture quite warm, but not boiling. Set aside.
In a second heavy bottomed pan, with sides at least 4 inches high, combine the sugar, both syrups and water. Stir until the sugars are melted, Then let it boil until it reaches 244 degrees (the soft ball point on a candy thermometer). Then very carefully add the cream and pumpkin mixture, and slowly bring this mixture to 240 degrees as registered on a on a candy thermometer. This can take awhile -- like 30 minutes -- but don't leave the kitchen, watch it carefully and stir it more frequently once it hits 230 degrees to keep it from burning at the bottom of the pan.
As soon as it reaches the 240, pull it off the heat and stir in the butter and lemon juice. Stir vigorously so that butter is fully incorporated.
Pour the mixture into the prepared pan. Let cool 30 minutes and sprinkle the salt over the top. Let the caramels fully set (at least 2 hours) before using a hot knife to cut them into 1-inch squares and wrapping them individually in waxed paper.