When I substitute tofu for ricotta in lasagna I use this recipe:
1 lb firm tofu, pressed
1 tablespoon garlic powder
1 teaspoon oregano
1 teaspoon basil
1 teaspoon lemon juice
1 tablespoon olive oil
I freeze the tofu then defrost it in the fridge. Make sure you press the water out by putting it under a plate with something heavy on top (freezing it helps get more of the water out).
In a large bowl, mush the tofu up with your hands, till it's crumbly.
Add lemon juice, garlic powder, oregeno, and basil. Mush with hands again, this time you want it to get very mushy so squeeze through your fingers and mush until it reaches the consistency of ricotta cheese. May take 2-5 minutes.
Add olive oil, stir with fork. Cover and refigerate until ready to use.
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