Roll out your pie crust and using an appropriate size glass, cut out your circles. Place them on the overturned mini cupcake tin and pinch the sides so they form to the pan. If you don't have mini cupcake tins, you can use a regular cupcake/muffin pans right side up but you'll need to stack an additional pan over the cut outs so they keep the cup shape when baking - don't forget to use a nonstick spray.
Bake at 400°F for 10-12 minutes until brown. Allow to cool slightly before removing from pans. You may need a fork to help lift off the cup. To get a nice sheen on the cups, brush with milk or egg wash prior to baking.
For the filling:
Start by getting your potatoes washed and cut (usually in ¼) and in a pot of boiling water. These can cook while you prepare everything else. I use yellow potatoes because the skin is soft, mashes well, and then I don't have to peel them. I also like that they have a softer texture than Russet but if that's what you have in your pantry, go for it, but peel them first.
In a large sauté pan, heat 2 tablespoons of olive oil and sauté the onions until translucent, over medium-high heat. Season with a pinch of salt.
Reduce heat to medium and add the ground beef to the cooked onions. Scramble beef and onions together, constantly stirring so you don't end up with any large chunks. Cook until beef just turns brown, a little pink is ok too as the heat will still be on while you add the potatoes.
Once the potatoes are cooked (soft and mashable, but not too squishy) add a few at a time and mash with a fork. Stir the mashed potato into the mix to incorporate before adding more potatoes to be mashed. Once all the potatoes are incorporated, mix well and season with salt and pepper to taste (about 1 ½ teaspoon salt and ½-1 tablespoon pepper for me.)
Build the cups:
Now, the next step is a real question of debate for me. In my opinion, you can go ahead and ruin all your hard work and put a small dab of mustard at the bottom of your cups or you can serve it them way I grew up on and put a little ketchup. Since we are super bowling with my in-laws today, I opted for their preferred version of mustard...
Using a long-line fork, carefully add your mix (also called 'Gorton') to the cups. For an appealing color on top, drizzle a little more of your preferred condiment or get fancy pants and sprinkle with chopped parsley.