lemon rind, grated
1CAKE: Butter and flour the bottom and sides of a 9 inch spring form pan; set aside.
2In a large bowl beat whites and cream of tartar to soft peaks; gradually beat in 1/4 cup of the sugar, continuing to beat to stiff peaks.
3In a separate bowl beat the yolks with remaining sugar until light yellow and thickened; scrape yolks over whites, add lemon rind and vanilla and fold together.
4Sift flour and salt over batter, folding in gently but thoroughly; transfer to prepared pan and bake at 350 for 25 minutes or until the top springs back when lightly touched.
5Let cool in pan on wire rack - If making ahead, remove from pan and wrap well for storage at cool room temperature for one to two days or in the freezer for up to 2 months.
6MOUSSE: In a very small saucepan sprinkle gelatin over water; set aside.
7Rinse, hull and puree berries.
8In a small saucepan combine puree, sugar and lemon juice and heat gently just long enough to dissolve sugar; remove from heat.
9Warm softened gelatin over low heat until clear and syrupy; stir into strawberry mixture.
10Transfer to a large bowl and chill to consistency of raw egg white; whisk in the yogurt.
11Whip cream until form; fold into mousse and return to fridge.
12SYRUP: In a small saucepan bring water and sugar to a boil; remove from heat, cool and stir in liqueur.
13ASSEMBLY: Using a long serrated knife, but cake into 2 thin layers; place top half, but side up, in the bottom of a clean 9 inch spring for pan. .
14Drizzle half the syrup evenly over the cut side of each of the 2 halves.
15Spoon strawberry mousse over cake in pan; don't worry if mousse extends over the sides.
16Set remaining layer, cut side over mousse, pressing gently; cover and chill thoroughly, overnight if possible.
17Release sides of pan, and using a wide lifter, transfer cake to service plate, doily-lined if you've thought that for ahead.
18CREAM FROSING AND GARNISH: Rinse and hull berries; slice thinly.
19Whip cream until it's stiff and firm; sweeten with sugar and spread evenly over top and sides of cake.
20Arrange berry slices in circle around the top and bottom edges of the cake; refrigerate until serving time, which should be within the following hour or two.