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1
To make streusel mixture, in a food processor or a bowl, whirl or mix 3/4 cup flour, 3/4 cup brown sugar, and 1/4 teaspoon salt.
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2
Cut 1/4 cup cold butter into chunks and add to bowl; pulse mixture or cut in butter with a pastry blender until mixture resembles coarse crumbs.
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3
Set aside.
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4
(Note: to save time in the morning when you are making these, you could do the streusel up to a few days ahead, and store in a zipped baggy in the refrigerator).
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5
In a bowl, with a mixer on high speed, beat remaining 1/4 cup butter and remaining 1 cup brown sugar until smooth.
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6
Beat in eggs and vanilla, scraping down sides of bowl as necessary, until well blended.
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7
Beat in mashed bananas.
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8
In a small bowl, stir together remaining 1 1/2 cups flour, baking powder, and remaining 1/4 teaspoon salt.
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9
Stir into banana mixture.
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10
Gently fold in sour cream until well blended.
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11
Grease and flour muffin pans: either a 6-cup jumbo muffin pan, or 18 regular muffin cups.
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12
Divide batter equally among the 6 jumbo (1-cup capacity) or 18 regular (1/3-cup capacity) pans, filling each halfway.
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13
Sprinkle streusel evenly over tops of cakes (crumble the streusel first if it sticks together).
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14
Bake in a 350 regular or convection oven until streusel is browned and a wooden skewer inserted into the center of a cake comes out with moist crumbs attached, 18 to 25 minutes.
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15
Cool 5 minutes in cups, then invert pan to remove.
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16
Serve warm or let cool completely.
