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1
Preheat oven to 350u00b0F and position rack in center of oven.
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2
Grease a 9-inch springform pan with butter and line the bottom with parchment paper, then grease parchment with butter.
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3
If using whole almonds, process in a food processor until finely ground. Sift ground almonds through a flour sifter; set aside coarse almond pieces that don't pass through sifter for another use. You should have 1 3/4 cups almond flour. Alternatively, if using store-bought almond flour, proceed to Step 4.
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4
In the bowl of a stand mixer fitted with the paddle, beat egg yolks, 1/2 cup honey, vanilla bean, baking soda, and salt until well combined and lightened in color, about 5 minutes. Add almond flour and beat at low speed until combined, about 1 minute longer.
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5
Using a clean stand-mixer bowl and the whisk attachment, whisk the egg whites at low speed until foamy. Add 2-3 drops of lemon juice, increase mixer speed to medium, and mix until soft peaks form, about 10 minutes.
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6
Fold 1/3 of beaten egg whites into almond flour batter, stirring well to thoroughly incorporate. Fold half of remaining egg whites into batter as gently as possible, being careful not to deflate whites. Repeat with remaining egg whites.
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7
Scrape batter into the prepared pan. Bake for 25 minutes (do not open the oven or move the cake during this time, as it can fall). Rotate cake gently and bake until cake feels solid in the middle when tapped and is a uniform dark brown color, about 10 minutes longer. Meanwhile, warm remaining 2 tablespoons honey in a small saucepan or microwave.
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8
Brush cake with warmed honey as soon as it comes out of the oven. Remove the springform pan's outer ring and let cake stand until cool. Decorate cake top with sliced almonds, if desired. Serve once cooled. Cake can be stored overnight at room temperature before serving.
