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1
Brown the butter. In a medium saucepan, melt the butter over medium heat. The butter will foam as the water content evaporates; continue to cook the butter, swirling the pan every 15 to 30 seconds, until the foaming subsides and the butter starts to smell nutty. The moment that brown particles start to appear at the bottom of the saucepan, pull it off the heat but continue to swirl the pan for about 15 seconds.
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2
Off the heat, drop the pecans into the butter. This will cool the temperature of the butter (preventing it from burning and making it easier to handle) and add a roasted note to the pecans by frying them. Let the mixture sit for about 3-4 minutes.
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3
Add all the pecans and butter to a food processor, making sure you scrape all the brown bits at the bottom of the pan into the food processor as well.. Process until very smooth, about 5 minutes.
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4
While you wait for the pecan butter to come together, prepare the dry ice. Wrap in a towel, and use a rolling pin or some other club-like implement (I used a baseball bat) to pulverize the dry ice into a powder. It's okay if some chunks remain.
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5
With the food processor running, drop in the salt through the spout. Slowly drizzle the maple syrup through the spout. Follow that with the milk.
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6
With the food processor running, add the dry ice one spoonful at a time through the spout. The dry ice will produce vapors out of the spout. DO NOT COVER THE SPOUT BETWEEN ADDITIONS. If you add too much as once, the mixture will bubble out of the spout; wait for most of the vapor coming out of the spout to dissipate before adding another spoonful.
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7
When the food processor begins to struggle, turn it off and quickly scoop out the ice cream into a freezable container, preferably one that has already been thoroughly chilled. Place the container in the freezer.
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8
Every couple of hours, you will need to stir the ice cream to help the excess carbon dioxide sublimate out. Otherwise, your ice cream will taste carbonated. Alternatively, you can let it sit in the freezer and let it release the excess gas on its own, but from past experience this can take up to a week.
