How to Make It
Preheat oven to 450°F. Trim base of cauliflower so it stands flat on a foil-lined baking sheet. Mix oil, Dijon, garlic, salt, and pepper in a small bowl and rub paste all over cauliflower. Roast until brown and tender, 50 to 55 minutes. Let cool completely. Reduce heat to 400°F.
On a lightly floured surface, unroll pastry sheet. Top evenly with chopped parsley, and gently flatten with a rolling pin to adhere parsley leaves. Brush with egg wash. Drape dough, parsley-side up, over the cooled cauliflower, tucking dough around the base. Bake until golden, 35 to 40 minutes.
To make the gravy, melt the butter in a medium saucepan over medium heat. Add the shallot and garlic and cook, stirring often, until softened, about 3 minutes. Whisk in flour, stirring, and cook until golden, about 2 minutes. Whisk in broth and simmer until thickened, 8 to 10 minutes. Stir in tamari and season with salt and pepper. Slice or cut cauliflower into wedges and serve with gravy.
Make-ahead! To reheat, place in a 350°F oven for 20 to 25 minutes until crispy and heated-through.