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1
Preheat oven to 400 degrees.
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2
Put a pan over medium heat and add 1 tablespoon olive oil and 1 tablespoon butter.
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3
Once the butter starts to froth, put the thinly sliced red onions in and turn the heat down to low.
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4
Cook, stirring often, until the onions have become translucent. This will take about 10 minutes but keep an eye on them.
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5
Add the sugar and the balsamic vinegar to the onions and cook on low, stirring often for about 10 minutes until the onion mixture is sticky and the liquid thickened up.
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6
Set the onions aside to cool.
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7
Melt the remaining butter in another pan and cook the mushrooms for a few minutes until they have just started to change color.
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8
Set the mushrooms aside to cool.
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9
Whilst the onions and mushrooms are cooling, layout your pie dough. You want the dough to be about as thick as a pinkie. If your pre-rolled dough is thicker roll it out to the desired thickness.
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10
Using a round cookie cutter or a glass, cut out 12 rounds of the dough.
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11
Press each round of dough into a hole of a 12 yield muffin tin. If your pan usually sticks, spray each hole with cooking spray before hand.
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12
Next, put the egg and sour cream into a bowl with the salt and pepper and beat together.
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13
Stir through the dried parsley and crumbled blue cheese. Set aside.
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14
Spoon a bit of the balsamic onions into the base of each tart.
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15
Top the onions with the mushrooms, trying to cover as much of the surface as possible.
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16
Spoon the blue cheese mixture over the top of each tart.
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17
Put tarts in the oven and bake for about 15 minutes until the pastry has gone golden and the cheese mixture has set.
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18
Take out of the oven and allow to cool before serving so the cheese mixture can firm up a little bit.
