To make cake: Preheat oven to 350 degrees F. Lightly oil a 9-inch square pan or coat it with nonstick cooking spray. Dust with flour, shaking out the excess.

Sift cake flour, salt, baking powder and baking soda into a bowl and set aside.

Puree pears in a food processor or blender. Transfer to a large bowl. Melt butter over medium heat in a small saucepan. Cook, swirling the pan, until the butter turns a light brown, about 1 minute. Add to the pears, along with 3/4 cup sugar, buttermilk, oil, vanilla, lemon zest and egg yolk; whisk until smooth. Set aside.

Beat the 2 egg whites in the bowl of an electric mixer until soft peaks form. Continue beating and slowly add the remaining 2 tablespoons sugar. Beat until stiff but not dry peaks form.

With a rubber spatula, gently fold the reserved dry ingredients into the pear mixture alternately with the beaten egg whites, making three additions of the dry ingredients and two of the beaten whites. Pour the batter into the prepared pan. Bake for about 30 minutes, or until a cake tester inserted in the center of the cake comes out clean. Let cool in the pan for 5 minutes, then turn out onto a rack to cool, right-side up.

To make filling and assemble cake: Puree ricotta until smooth in a food processor or blender. Add the drained yogurt, orange zest and confectioners' sugar; blend to mix.

Melt preserves over low heat in a small saucepan. Strain into a small bowl and set aside.

Use a large serrated knife to slice the cake horizontally into 2 layers. Put the bottom layer on a cake plate, cut-side up. Spread a thin layer of ricotta filling (about 1/2 cup) over the bottom layer. Set aside 2 pints of strawberries to garnish the cake. Cut the remaining berries in half lengthwise.

Place a row of strawberry halves, points up and cut sides facing out, on the edge of the bottom layer. (Choose smaller strawberries that are the same height. Trim the base of the strawberries, if needed, to make them all of equal height.) Fill the center with strawberry halves, cut sides facing down. Spread the remaining ricotta filling evenly over the strawberries in the center of the cake.

Set the top layer, cut-side down, on the filled cake. Press gently on the cake to level it. Brush a thin layer of strained preserves over the cake. Arrange whole strawberries in rows on top of the cake. Brush the strawberries with the strained preserves.