Sounds sort of like my recipe for tamale pie. If your recipe instructed you to "pour" the cornmeal mixture for the top and bottom crusts, right there is where it went wrong. The cornmeal mush/polenta or whatever you call it should not be pourable. A consistency that's spreadable or pat-able is okay; pourable is not good.

Also, the cornmeal mixture should be no more than a half-inch thick on the top and bottom, so pan size has to be adjusted accordingly. The mixture won't be dry and crumbly like cornbread--it should be moist but firm, like, well, a tamale.

If you're up to doing it again, try this:

In a medium saucepan, stir together 1-1/2 cups yellow cornmeal, 1 tablespoon all-purpose flour and 2 teaspoons Kosher salt. Slowly add 4 cups of water, whisking constantly so that there are no lumps in the mixture. (If the recipe for your filling calls for a can of corn, use that liquid to replace an equal amount of water.) Cook over medium-high heat, whisking frequently, until the mixture begins to boil. Turn the heat to low and cook, whisking constantly, for 5 minutes or until the mixture is very thick but still spreadable, like wallpaper paste. Remove from heat and stir in 4 tablespoons (1/4 cup or 1/2 stick) butter until melted. Butter a 12"x8" casserole or 13" x 9" baking dish. Spread or pat half the cornmeal mixture over the bottom of the dish; add your filling, enough to make a layer 1-1/2" to 2" thick; dot, spread or pat the remaining cormeal mixture evenly over the filling. Bake at 350 degrees until the filling is bubbly, about half an hour to 40 minutes. Top with shredded cheddar cheese when you think there's 10 minutes' baking time left.

I appreciate all this very valuable input. DonnyG is correct in that it's polenta, which I've made before. The finished dish isn't supposed to be a crumble, but even that would have been better than what I got! Instructions were to pour some of the cooked cornmeal on the bottom of the pie plate, add the ground meat mixture and then pour the remaining cornmeal over the top. I assumed it would turn into a crust of some sort because the final instruction is "cut into pie-shaped wedges and serve hot." To answer cookbookchick, no, it isn't good enough to try again with a re-worked topping. I just put it in the "bad recipe" file, which is heading to the shredder.

How was the rest of the dish -- worth trying to rework the topping next time?

I agree with all. What it sounds like you made is polenta which will never firm to a crumble or crust. Is it supposed to be a crumble? If so I would just add a little melted butter to corn meal until you can make a dry ball in your hand and spread over the top and let the oven do the cooking.

I'm in concurrence with the previous two answers, and to me it also sounds like "the recipe" maybe flawed itself. Is the end result supposed to resemble polenta or grits or be more fluffy like corn bread. If you rest cooked polenta overnight, covered, you can bake it into something firm the next day. It would be a tricky but not impossible step to cut it to pie shape, rest and then bake.

If it was just cooked cornmeal (with no flour, eggs, baking powder or anything to hold it together) it would be like plain polenta--hard to thicken it unless you really cook it down or use less liquid on top of the stove, and it probably wouldn't change that much once it went into the oven--it would thicken a little, but not that much if it had a runny filling (chili?) on the bottom.

I don't think freshness is a factor here - in my experience, freshness is something you're likely to taste (the cornmeal will taste off or rancid).

Was the topping still very runny? If so perhaps you didn't let it thicken up enough. (personally I hate instructions like "cook until thickened" because they're so relative. I like "cook until coats a spoon" or "cook until thick enough for a spoon to stand up in the pot", etc.)

Could your oven temp be off? Maybe the temp wasn't high enough to set the cornmeal.

Or it could just be a badly tested recipe and even following the instructions, it might not have worked.