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1
Heat oven to 350 degrees.
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2
Grease a 9-by-5-inch loaf pan, then line with parchment paper, leaving enough to hang over the edges of the pan.
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3
Grease the parchment on the bottom of the loaf pan.
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4
In a heatproof bowl set over a pan of simmering water, or in the microwave, melt the chocolate for the cake, stirring until smooth.
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5
Set aside to cool while you prepare the streusel.
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6
Prepare the streusel: In a bowl, stir together flour, sugar, cocoa powder and salt.
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7
Using fingers or a fork, cut in the butter until it is evenly distributed and forms large, moist crumbs.
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8
Stir in the chocolate chips.
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9
Scatter half the streusel evenly into the bottom of the loaf pan.
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10
Bake for 15 to 18 minutes, or until baked through.
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11
Prepare the cake: In a large bowl, sift together flour, cocoa powder, baking powder and baking soda.
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12
In the bowl of an electric mixer fitted with the whisk attachment, beat melted butter, both sugars and salt together until combined.
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13
Beat in egg, vanilla extract, yogurt, milk and melted chocolate.
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14
Fold in dry ingredients until just combined.
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15
Scrape batter into prepared pan and top with remaining streusel.
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16
Bake until a toothpick inserted in the center of cake emerges clean, about 1 hour 15 minutes.
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17
Transfer pan to a wire rack and cool completely before turning out and slicing.
