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1
Cover husks with hot water by 2 inches in a large bowl and soak, kept submerged with an inverted plate, turning husks occasionally, until soft, about 30 minutes.
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2
Rinse husks, 1 at a time, under running water.
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3
Pile 24 of largest husks on a plate and cover with a dampened kitchen towel.
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4
Tear some of remaining husks lengthwise into 24 (1/2-inch-wide) strips to use as ties (keep damp as well).
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5
Cover porcini with 1 cup very hot water in a small bowl and soak 30 minutes.
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6
Lift out porcini, squeezing liquid back into bowl (reserve liquid), then rinse mushrooms to remove any grit.
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7
Coarsely chop porcini.
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8
Pour soaking liquid through a paper-towel-lined sieve into a glass measure and reserve.
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9
Heat 1/2 stick butter in a 12-inch heavy nonstick skillet over high heat until foam subsides, then saute onion and garlic, stirring, 1 minute.
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10
Add mushrooms (including porcini) and epazote (if using) and saute, stirring occasionally, until liquid is released, about 3 minutes.
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11
Add porcini soaking liquid and simmer, stirring occasionally, until most of liquid is evaporated and mushrooms are slightly browned, 3 to 5 minutes, then sprinkle with pepper and 1/2 teaspoon salt.
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12
Transfer to a bowl to cool.
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13
Beat remaining 1 1/2 sticks butter with an electric mixer at medium-high speed until light and fluffy, about 30 seconds.
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14
Sift masa harina with baking powder, sugar, and remaining 1 1/2 teaspoons salt into a bowl.
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15
Stir in 1 1/2 cups very hot water until a thick paste forms.
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16
Beat masa mixture into butter in 3 batches, beating until smooth after each addition.
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17
Reduce speed to low and mix in mushroom mixture until just combined.
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18
Put 1 husk on a work surface, pointed end closest to you, and, spreading it flat, mound 3 tablespoons filling in center and flatten slightly into a rough oval (about 1/2 inch thick) with back of a spoon, leaving a 1-inch border on both sides.
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19
Bring pointed end of husk up over mound of filling to cover, and fold sides of husk over filling to enclose.
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20
Gather together open end of husk at top of filling, creating a flat pouch, and tie with a corn-husk strip.
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21
Assemble 23 more tamales in same manner.
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22
Arrange tamales upright in 1 layer in steamer insert so they resemble falling dominoes in rows.
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23
Set steamer over boiling water in pot and cover with a folded kitchen towel (towel absorbs condensation so tamales don't get soggy).
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24
Steam tamales, tightly covered with a lid, adding more water as necessary, until filling is tender, about 30 minutes.
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25
To check for doneness, open 1 steamed tamale and if any part of filling is still gummy, steam 5 to 10 minutes more.
