Mix the butter and icing sugar until fluffy. Gradually beat in the flour. Press the mixture onto the bottom and sides of a greased tart tin. Bake 30-35 minutes at 150 degrees C or until browning. Let cool on a wire rack.
Melt the chocolate in the microwave or over a double boiler. Mix in the mascarpone until smooth. Stir in the lemon zest.
Once the crust has cooled, spread the chocolate mixture evenly over the bottom. Chill 30 minutes in the fridge.
Cut the strawberries into thin slices. Peel and thinly slice the pear (sprinkle with a little lemon juice to prevent browning).
Arrange the fruit in circles over the filling, starting at the outer edge. Raspberries at the outer rim, overlapped with strawberry slices, then pear, and in the middle a handful of blueberries. Store in the fridge until serving.