Spray the bottom of an 11" by 16" or 9" x 13" baking pan with nonstick spray and line it with parchment paper.
Sift together the flour, baking powder and salt.
Whisk together the egg yolks and sugar using a hand held or standing mixer on high speed until thick and smooth. This will take about one minute for a standing mixer, three minutes for a hand held. Reduce to low speed and add the hot water and the vanilla. Scrape down the sides of the mixer bowl. Again increase to high speed and whip until thick and ribbony.
On low speed add the dry ingredients a little at a time until incorporated.
In a clean bowl, whisk the egg whites until soft peaks form. Fold the egg whites into the batter. Spread the batter evenly and gently into the prepared pan.
Bake the cake for about 20 minutes until it is golden brown in color and springs back lightly when touched on top. Cool the cake. Remove it from the pan by running a knife around the inside edge of the cake pan and inverting it onto the counter. Carefully peel off the parchment paper.
Blueberry Compote
Place half the blueberries and the sugar in a small heavy bottomed saucepan.
Cook, stirring frequently, over medium low heat until the sugar is dissolved and the blueberries pop and give off some juice. Stir in the remaining blueberries. Cool to room temperature.
Assembling the trifle:
Peel and pit the peaches. Slice them into one-inch slices. Place them in a bowl and mash them roughly with a potato masher or very roughly chop them in the food processor. Stir in the sugar. Combine the sour cream and cream.
Cut the cake into quarters and each quarter in half horizontally.
Place a large spoonful of the blueberry compote in the bottom of a 2 ½ quart glass bowl or attractive serving dish.
Cut cake pieces to fit in a single layer over the compote. Cover the cake with ¼ of the blueberry compote, ¼ of the peaches and then ¼ of the cream.
Repeat layering all the ingredients three more times, finishing with the cream. (There will be a little cake leftover.)
Cover the trifle with saran wrap. Refrigerate the trifle for at least six hours to overnight.
Planning Ahead
The cake can be made several days in advance. Store wrapped in plastic wrap at room temperature. The cake is actually easier to cut if it is a day old. The blueberry compote can be made a day or two in advance.
The trifle can be assembled a day before you plan to serve it.