Slice the tomatoes. Set aside, and place on a paper towel to drain while preparing other ingredients. You can use salt here to draw out even more moisture if you wish.
Set one sheet of puff pastry out to thaw.
Prepare the grits according to package directions. When done, mix in ½ cup cheese.
Preheat oven to 375 F.
Heat 1 teaspoon of olive oil in a small saute pan over medium high heat. Add the onions and saute for 5 minutes or until beginning to lightly brown. Set aside, off heat, once done.
Mix together the remaining cheese, mayonnaise, herbs, and seasonings.
Now it's time to assemble. Spray a 2 quart capacity casserole dish. Spread the grits on the bottom of the dish in an even layer.
Scatter the sauteed onions evenly across the grits.
Layer the tomatoes on top of the onions, overlapping a bit as necessary.
Spread the cheese mayo mixture on top of the tomatoes. I use my fingers and try to evenly drop blobs around the top rather than trying to spread it with an offset spatula.
Finally, use a knife or scissors to cut the puff pastry into pieces to where it covers as much as possible of the top of the casserole dish. You may only need ⅔ of the sheet, like I did, or you may need the whole thing. Try not to overlap the puff pastry here if possible.
Bake the casserole for 30 minutes, and an additional 10 minutes if needed to lightly brown the top. Remove from oven and let rest for 5-10 minutes.
Serve immediately. You can reheat the leftovers, but only for 1 day, otherwise it gets too soggy.
