Center a rack in the oven and preheat the oven to 350°F. Generously butter a 9-inch springform pan, fit the bottom with a circle of parchment or wax paper and place it on a baking sheet lined with parchment paper or a silicone baking mat (the just-in-case drip-catcher).

Whisk the flour, baking powder and salt together.

Working in a large bowl, whisk the sugar and yogurt together until smooth. Whisking vigorously, add the egg and the yolk; whisk in the vanilla extract. Switch to a flexible spatula and stir the flour mixture into the batter. When the dry ingredients are fully incorporated, gradually fold in the oil. Pour the batter into the springform pan and tilt and rotate the pan so that the batter evenly covers the bottom of the pan - you'll have a thin layer.

Bake the cake for 23 to 25 minutes, or until it is golden brown, springy to the touch and a tester inserted into the center of the cake comes out clean. Place the pan on a cooling rack, wait 5 minutes, and then release the sides, invert the cake onto the rack, lift off the base, carefully peel away the paper and turn the cake over; allow it to come to room temperature. Wash and dry the springform, you'll use it to mold the shortcake. (You can make the cake up to 2 days in advance and keep it wrapped in plastic at room temperature.)

When you're ready to make the mousse, return the cake to the springform pan.

Using a blender (regular or immersion) or a food processor, puree 3/4 pound (about 3 cups) of the strawberries; you should have 1 cup of puree. Cut the remaining berries into small cubes and keep both aside.

Place the chocolate in a large heatproof bowl over (not touching) a saucepan of gently simmering water. Heat the chocolate until it is just melted - stay close because white chocolate will hold its shape even when it's melted, so you must be careful not to scorch it. When the chocolate is melted, turn off the heat, but keep the bowl over the hot water.

Meanwhile, put the gelatin in a small microwave-safe bowl and pour over the cold water. Let sit for 5 minutes, or until the water is absorbed and the gelatin has expanded, then heat the gelatin in a microwave oven for 20 seconds, until completely liquefied.

Using a whisk, stir the chocolate until it is smooth. Add the dissolved gelatin and then whisk like mad to incorporate it and smooth the mixture once again. Keep the bowl over the water, pour in the berry puree and whisk to blend. Transfer the bowl to the counter.

Whip the heavy cream until it holds soft peaks. Gradually add the confectioners' sugar and continue to beat until the cream holds medium-firm peaks; keep at hand.

Working quickly (so that the colder ingredients don't set the gelatin), whisk the yogurt into the chocolate-strawberry mixture in three additions. Don't be afraid to whisk energetically. Stir in the liqueur, if you're using it.

Switch to a flexible spatula and gently fold in the whipped cream. When the cream is almost fully incorporated, add the diced strawberries and finish blending.

Pour the mousse over the cake in the springform pan and jiggle the pan so that the mousse shimmies down into the space between the cake and the pan; smooth the top.

Chill the cake for at least 6 hours or for as long as 2 days. After 1 hour in the fridge, cover the cake with plastic wrap, taking care not to let the plastic touch the mousse.

It's hard to say exactly how many berries you'll need, so start with 15 and cut more if and when you need them. Hull the berries, stand them up and, working with a thin-bladed knife, cut them into slices about 1/8 inch thick; you'll get 5 to 6 slices from each berry. Set the ends aside. Working from the outside of the cake in, make concentric circles of slightly overlapping berries, keeping the points of the berries facing out and the flat bases facing in. For the first circle, choose the tallest slices of berries and lay them, slightly overlapping, flat against the mousse. The decoration is prettiest if each subsequent circle is made from shorter and shorter slices of berries. For the next and the remaining circles - you'll have a total of 5 to 6 concentric circles - overlap the berries, but lean them against the previous circle and position them so that they stand up a bit. Keep the circles snug and work until you have a small circle of bare mousse at the center. Slice the set-aside ends of the berries (or coarsely chop them) and pile them in the center of the cake.

For an extra bit of festiveness, you can lightly glaze the berries. Put about 1/4 cup of jelly and a splash of water in a microwave-safe bowl, cover and heat until the jelly is melted, about 30 seconds. If you have a pastry brush, use it to dab a little jelly on the berries - go lightly. Alternatively, you can drizzle some jelly on the berries from the tip of a small spoon.

Because the cake has been out of the refrigerator for a while, return it to the fridge for another 30 minutes to firm before serving.

When you're ready to serve, warm the outside of the springform pan using a hairdryer (my favorite tool for this). Alternatively, you can wrap the pan in warm, damp kitchen towels. Very carefully remove the sides of the pan. Keep the cake on the base (or remove the base if you're dexterous) and transfer it to a platter for serving.

For more Strawberry Shortcake recipes, click here!