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1
Getting ready: Center a rack in the oven and preheat the oven to 350 degrees.
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Butter an 8x8-inch pan (Pyrex is great for this) and put it on a lined baking sheet.
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3
To make the crumbs: Put all the ingredients except the nuts in a food processor and pulse just until the mixture forms clumps and curds and holds together when pressed.
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4
Scrape the topping into a bowl, stir in the nuts and press a piece of plastic against the surface.
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5
Refrigerate until needed.
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6
(Covered well, the crumb mix can be refrigerated for about 3 days.)
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7
To make the cake batter: Using your fingertips, toss the blueberries and 2 teaspoons of the flour together just to coat the berries; set aside.
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8
Whisk together the remaining 2 cups flour, the baking powder, soda, salt, cinnamon and nutmeg.
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9
Working in the bowl of a stand mixer or in another large bowl, rub the sugar and zest together with your fingertips until the sugar is moist and aromatic.
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10
Add the butter and, with the paddle or whisk attachment, or with a hand mixer, beat the sugar with the butter at medium speed until light, about 3 minutes.
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11
Add the eggs one by one, beating for about 1 minute after each addition, then beat in the vanilla extract.
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12
Dont be concerned if the batter looks curdled it will soon smooth out.
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Reduce the mixer speed to low and add the flour mixture and the buttermilk alternately, the flour in 3 parts, the buttermilk in 2 (begin and end with the dry ingredients).
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14
You will have a thick, creamy batter.
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15
With a rubber spatula, gently stir in the berries.
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16
Scrape the batter into the buttered pan and smooth the top gently with the spatula.
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17
Pull the crumb mix from the refrigerator and, working with your fingertips, break it into pieces.
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Theres no need to try to get even pieces these are crumbs and theyre supposed to be lumpy and bumpy and every shape and size.
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19
Scatter the crumbs over the batter, pressing them down ever so slightly.
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20
Slide the sheet into the oven and bake 55 to 65 minutes, or until the crumbs are golden and a knife inserted into the center of the cake comes out clean.
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21
Transfer the cake to a rack and cool just until it is warm or until it reaches room temperature.
