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1
Line baking sheet with aluminum foil; brush foil with vegetable oil.
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2
Stir maple syrup, sugar, and apple cider vinegar in heavy medium saucepan until sugar is moistened.
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3
Attach candy thermometer.
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4
Without stirring, bring mixture to boil over medium-high heat and boil until temperature registers 300F, occasionally brushing down pan sides with wet pastry brush and swirling pan, about 7 minutes.
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5
Remove pan from heat; mix in baking soda, then nuts (mixture will foam up).
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6
Immediately pour maple candy out onto prepared baking sheet and spread to even 1/2-inch thickness (candy begins to firm quickly).
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7
Let stand until candy hardens, at least 30 minutes.
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8
(Can be made 1 day ahead.
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9
Cover baking sheet tightly with plastic wrap and store candy at room temperature.)
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10
Preheat oven to 350F.
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11
Spray two 8-inch-diameter cake pans with 2-inch-high sides with nonstick spray.
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12
Line pan bottoms with parchment paper; spray parchment.
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13
Whisk flour, baking powder, baking soda, salt, and cinnamon in medium bowl to blend.
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14
Using electric mixer, beat butter in large bowl until fluffy.
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15
Add golden brown sugar and beat until blended and fluffy.
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16
Gradually beat in maple syrup (batter may look curdled).
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17
Beat in eggs 1 at a time, then vanilla extract.
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18
Beat in dry ingredients in 3 additions alternately with buttermilk in 2 additions.
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19
Divide batter between prepared pans.
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20
Bake cakes until tester inserted into center comes out clean, about 30 minutes.
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21
Cool cakes 5 minutes.
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22
Turn cakes out onto racks, peel off parchment paper, and cool cakes completely.
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23
(Can be made 1 day ahead.
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24
Wrap tightly; store at room temperature.)
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25
Bring maple syrup to boil in small saucepan.
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26
Meanwhile, using electric mixer, beat egg whites in large bowl until stiff peaks form.
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27
Without letting hot maple syrup touch beaters, pour 1/4 cup syrup into egg whites, beating to blend.
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28
Gradually beat in remaining hot maple syrup.
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29
Continue to beat until whites are stiff and cool, about 15 minutes.
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30
Add butter, 1 slice at a time, beating to blend after each addition (buttercream may deflate and separate; keep beating until smooth again).
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31
Chop enough maple candy into 1/4-inch pieces to measure 1 cup; wrap remaining maple candy tightly in plastic.
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32
Place 1 cake layer on platter.
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33
Spread 1 cup buttercream over cake.
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34
Sprinkle with 1 cup maple candy pieces; press candy lightly to adhere.
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35
Top with second cake layer.
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36
Spread remaining buttercream smoothly over top and sides of cake.
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37
(Can be made 1 day ahead.
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38
Cover with cake dome; chill.
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39
Bring to room temperature before continuing.)
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40
Chop enough of remaining maple candy into 1/4-inch pieces to measure 2 cups.
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41
Mince enough maple candy to measure 2 tablespoons.
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42
Press 1/4-inch pieces onto sides of cake.
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43
Sprinkle minced maple candy on top edge.
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44
Serve cake within 2 hours.
