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1
Preheat oven to 350F.
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2
In a baking pan toast nuts in one layer in middle of oven 10 minutes, or until almonds are lightly colored and hazelnut skins are blistered.
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3
Wrap nuts in a kitchen towel and let steam 1 minute.
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4
Rub nuts in towel to remove any loose hazelnut skins (do not worry about skins that do not come off) and cool completely.
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5
Line a baking sheet with foil.
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6
In a small heavy saucepan bring sugar and water to a boil, stirring until sugar is dissolved.
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7
Boil syrup, without stirring, washing down any sugar crystals that cling to side of pan with a pastry brush dipped in cold water, until it begins to turn golden.
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8
Swirl pan until syrup is deep golden and remove from heat.
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9
Stir in nuts and pour praline onto baking sheet, spreading evenly.
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10
Cool praline completely and break into pieces.
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11
Transfer praline to a sealable plastic bag and with a rolling pin coarsely crush.
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12
Preheat oven to 300F.
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13
Generously butter a 9-inch round cake pan (at least 2 inches deep) and line bottom with wax or parchment paper.
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14
Butter paper and dust pan with flour, knocking out excess.
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15
Finely chop chocolate.
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16
In a small saucepan combine cocoa powder, butter, oil, and water.
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17
Bring mixture to a boil, stirring until smooth, and remove pan from heat.
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18
Add chocolate and sugar, whisking until smooth, and transfer to a bowl.
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19
Cool chocolate mixture completely and whisk in egg.
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20
Sift flour and baking powder over chocolate mixture and whisk until just combined.
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21
Whisk in buttermilk and pour batter into cake pan, spreading evenly.
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22
Bake cake in middle of oven 45 to 50 minutes, or until a tester comes out clean, and cool in pan on a rack 5 minutes.
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23
Run a thin knife around edge of pan and invert cake onto rack.
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24
Discard paper.
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25
Cool cake completely and transfer to a plate.
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26
In a bowl stir together mascarpone and sugar.
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27
Spread mixture over top of cake and generously sprinkle with praline.
