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1
Preheat oven to 350F.
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2
Butter an 8-inch round cake pan; line bottom with a round of waxed or parchment paper.
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3
Butter paper; dust bottom and sides of pan with cocoa, tapping out excess.
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4
Sift together cocoa, flour, baking powder, and salt.
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5
With an electric mixer on medium-high speed, cream butter and 1 cup sugar until light and fluffy.
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6
Add eggs one at a time, beating well after each and scraping down sides of bowl as needed.
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7
Beat in vanilla.
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8
Reduce speed to low.
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9
Add flour mixture in two batches, alternating with the sour cream and beginning and ending with the flour.
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10
Spread batter in prepared pan.
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11
Tap pan firmly on countertop once to eliminate large air bubbles.
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12
Bake until a cake tester inserted into the center comes out clean, 30 to 35 minutes.
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13
Cool 10 minutes in pan, then invert onto a wire rack to cool completely (bottom side up).
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14
Set rack with cake over a rimmed baking sheet.
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15
Pour glaze over cake, letting it run over sides; spread gently with an offset spatula or table knife to coat.
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16
Let set, about 30 minutes.
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17
If desired, whip cream and remaining 2 tablespoons sugar with an electric mixer until soft peaks form.
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18
Serve cake with whipped cream and chocolate shavings.
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19
Place chocolate in a medium bowl.
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20
In a saucepan, bring cream to a boil.
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21
Pour over chocolate; whisk until smooth.
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22
Let cool until thick yet pourable, 2 to 3 minutes.
