Set aside 1/3 cup blueberries for garnish. Combine remaining blueberries, ¼ cup sugar and vanilla in a zip-top plastic bag. Press with hands to crush berries; let stand 10 minutes.

Spread blueberry preserves on one side of cake slices. Cut cake into cubes and place in four parfait or other tall glasses. Whip cream to soft peaks with a wire whisk or electric mixer.

In another bowl, beat mascarpone, remaining 1/4 cup sugar and almond extract until light and fluffy. Gently fold whipped cream into mascarpone.

Spoon 2 tablespoons mascarpone mixture over cake cubes in each glass. Smooth surface of cream. Top each with 2 tablespoons crushed blueberries. Repeat layers.

Garnish with sliced almonds and reserved blueberries. Can be made up to 1 hour ahead and refrigerated.