In an electric mixer fitted with a whisk attachment, or you can use a hand mixer, combine the egg whites, cold water, cream of tartar, vanilla and almond extract. Beat on high until the mixture if stiff and glossy, but not dry. Fold in 3/4 cup of sugar 2 Tablespoons at a time.
Fold in flour and sugar mixture a little at a time. Bake the batter in an ungreased 10-inch tube pan about 45 minutes or until the cake is golden and a toothpick tester comes out clean when inserted into the center of the cake. Invert pan to cool.
Make filling by placing whipping cream in the bowl of a mixer fitted with a whisk attachment. Whip cream until soft peaks form. Slowly add the sugar. Stir blueberry jam until smooth (heating the jam slightly in the microwave may help). Combine the jam and Mascarpone, mix until uniform. Fold jam and Mascarpone cheese into the whipped cream until smooth. Chill in refrigerator while cake cools.
Once cake cools completely, remove cake by cutting around the edges and center tube and then around the bottom. Cut cake in half, horizontally, gently with a serrated knife. Form a trough by pulling out some of the cake in the center of the bottom half. Fill trough with blueberry filling. Place top half of cake over filling. Dust cake with confectioner's sugar and serve.