Whoa, I had no clue you could do this with a slow cooker! Yum!

1 medium whole cabbage
4 tablespoons unsalted butter
4 cloves garlic, minced
1/2 cup grated Parmesan cheese
1 lemon, zested and juiced
1 teaspoon salt
1/2 teaspoon black pepper
1 cup vegetable broth
Fresh parsley, chopped (for garnish)