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1
Cook frozen mixed berries and 6 tablespoons sugar in a heavy medium saucepan over medium heat until mixture resembles jam and is reduced to 1 cup, stirring frequently, about 15 minutes.
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2
Cool jam mixture.
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3
Strain syrup from thawed raspberries through sieve set over bowl, pressing gently on solids.
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4
Discard solids.
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5
Add raspberry liquer to raspberry syrup in bowl.
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6
Using sharp knife, trim 1 biscuit to 3-inch length.
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7
Quickly dip biscuit into syrup, turning to coat lightly.
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8
Place rounded end up and sugared side against side of a 9-inch springform pan with 2 3/4 inch sides.
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9
Repeat with as many biscuits as necessary to cover sides of pan.
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10
Dip more biscuits in syrup and arrange on bottom of pan, covering completely and trimming to fit.
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11
In bowl, whisk mascarpone with 6 tablespoons sugar and vanilla to blend.
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12
Set aside.
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13
Thinly slice enough strawberries to measure 1/2 cup.
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14
Gently spread half of jam mixture over biscuits in bottom of pan.
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15
Spoon half of mascarpone mixture over; smooth top.
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16
Sprinkle with sliced strawberries, 1/2 cup fresh raspberries and 1/2 cup blueberries.
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17
Dip more biscuits into syrop; arrange over fruit in pan, covering completely and trimming to fit.
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18
Gently spread remaining jam mixture over biscuits.
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19
Spoon remaining mascarpone mixture over; smooth top.
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20
Cover, chill at least 4 hours or overnight.
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21
Release pan sides.
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22
Transfer cake to platter.
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23
Arrange remaining fresh berries decoratively atop cake and serve.
