Set the Instant Pot to Sauté mode. Add the tallow or butter and sauté the onion for about 5 minutes, until softened and lightly golden. Add the garlic and cook for another 30 seconds, stirring constantly so it doesn't burn.
Add the paprika, cumin, coriander, turmeric, cinnamon, black pepper, and salt. Stir in the tomato paste and cook for about 1 minute, stirring constantly, until the spices are fragrant and the tomato paste is well incorporated.
Cancel the Sauté mode and stir in about 1 cup of bone broth. Use an immersion blender to blend everything until smooth. This creates a rich, creamy base for your tagine.
Add the gizzards, soaked and drained chickpeas, and enough bone broth to just cover everything. Stir well. Secure the lid and cook on High Pressure for 40 minutes. Allow the pressure to release naturally for 15 minutes, then carefully release any remaining pressure.
Open the lid and stir in the carrots and potatoes. Secure the lid again and cook on High Pressure for 4 minutes. When the cooking time is up, quick release the pressure.
Taste the tagine and adjust the salt if needed. Stir in some chopped cilantro and a squeeze of fresh lemon juice, if you like. Serve hot over couscous or in bowls with some flatbread for dipping.