In a large mixing bowl, add the masa corn flour, salt, and baking powder. While running a hand mixer on low, slowly pour in 3 cups of water until blended completely. Then, slowly pour in the the melted vegetable shortening while stirring.
Dry off the corn husks and spread on 3 tbsp of the masa mixture. Add 1½ tbsp of the picadillo on top of the masa. Fold in the sides of the corn husk, then fold the narrow end of the husk up. If you'd like you can tie the tamale shut with a strand torn from the husk. Otherwise, just make sure they're resting against each other in the Instant Pot in order to keep them closed.
Add the steamer rack to the bottom of the Instant Pot. Add 1 cup of water to the bottom and carefully arrange the tamales around the Instant Pot being careful to keep them closed and intact. Cover and make sure the vent valve is in the sealed position. Press the "Manual" button on the Instant Pot and set the cooking time to 45 minutes.
After the cooking time has ended, allow 10-15 minutes to let the steam release naturally. Carefully release any steam that might be left in the pot by holding a kitchen towel to open the steam vent. (Careful...any steam will be HOT!)
Allow the tamales to rest for 10-15 minutes before serving.