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1
Position rack in center of oven and preheat to 350F.
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2
Butter 9-inch-diameter springform pan with 2 3/4-inch-high sides.
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3
Dust pan lightly with flour, tap out excess.
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4
Melt unsweetened chocolate and butter in heavy small saucepan over low heat.
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5
Cool.
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6
Blend flour, salt and baking powder in small bowl.
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7
Using electric mixer, beat eggs and sugar in medium bowl until slowly dissolving ribbon forms when beaters are lifted, about 4 minutes.
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8
Scrape down sides of bowl.
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9
Beat in melted chocolate mixture, vanilla and chopped chocolate.
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10
Add dry ingredients and mix until just blended; do not over beat.
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11
Spread 1 cup brownie batter over bottom of prepared pan.
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12
Bake until firm, about 17 minutes.
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13
Cool baked bottom crust in pan in freezer, about 15 minutes.
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14
Maintain oven temperature.
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15
Blend cream cheese and sugar in processor until smooth.
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16
Add eggs and sour cream and process using on/off turns until mixture is smooth, stopping to scrape down sides of bowl as needed.
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17
Blend in peanut butter using on/off turns.
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18
Using small knife, spread remaining brownie batter evenly around sides of pan, sealing batter to bottom crust.
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19
Pour in filling, which will not be as high as brownie batter.
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20
Bake until center of cheesecake is gently set and brownie sides have fallen to form a 1-inch-wide ring around filling, about 30 minutes.
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21
Blend sour cream and sugar in small bowl.
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22
Spread evenly atop cheesecake to within 3/4 inch of edge.
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23
Bake cheesecake 1 more minute.
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24
Set cake on rack.
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25
Using small sharp knife, cut around top edge of cake to loosen from pan sides.
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26
Cool completely.
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27
Place peanut butter in pastry bag fitted with small (no.
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28
1) star tip.
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29
Pipe tiny rosettes of peanut butter around edge of sour cream.
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30
Refrigerate cake until rosettes are firm, about 30 minutes.
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31
Cover pan tightly with foil and chill overnight.
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32
(Can be prepared 1 day ahead.)
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33
Cut around pan sides to loosen cake.
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34
Release sides.
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35
Transfer cheesecake to platter.
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36
Cut into wedges and serve.