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1
Preheat the oven to 350F.
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2
Line two 12-cup standard muffin tins (2 1/2 inches top diameter and 1 1/4 inches deep) with paper liners.
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3
Set aside.
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4
Place 10 ounces of the bittersweet chocolate and the butter in a stainless bowl over simmering water to melt.
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5
Set aside.
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6
Put the egg yolks in the bowl of a stand mixer and whisk in 1/2 cup of sugar.
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7
Place the bowl over simmering water, and whisk until yolks reach about 120F.
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8
Mount the yolks on a stand mixer fitted with a whisk attachment.
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9
Whip at high speed until yolks triple in volume.
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10
Transfer the yolks into a 3 quart stainless bowl.
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11
Set aside.
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12
Place the whites in a clean bowl of a stand mixer fitted with the whisk attachment.
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13
Whip on medium speed until whites become frothy.
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14
Add cream of tartar and increase mixer speed to high.
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15
When the whites begin to form soft peaks, add 1 cup of sugar and continue to whip to a shinny firm peak.
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16
Using a spatula, fold the melted chocolate into the yolk mixture.
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17
Carefully fold in whites and flour in 3 additions.
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18
Fold in the milk and the remaining dark chocolate pieces, just until incorporated.
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19
Do not over-mix.
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20
Using a tablespoon, divide the batter evenly among the muffin cups, filling them about two-thirds full.
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21
Bake on the middle shelf of the oven until the top of the muffins form a crust, 20 to 25 minutes.
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22
Remove from oven, and allow to cool for 30 minutes.
