Preheat the oven to 400 degrees Fahrenheit. Set aside an 8- by 11- and- 1/2-inch rectangular tart pan with removable bottom. You can also use smaller tart pans and discard any extra dough.

Add the flour, sugar, baking powder and salt to the bowl of a stand mixer fitted with a dough hook, and mix until combined. Add the cold butter and mix until crumbly. Add the egg yolk, juice and zest and mix until it forms a ball.

Press the dough into the bottom and up the sides of your tart pan. Take extra care to press the dough evenly throughout. Use a straight sided, round dry-measuring cup to further compact the dough, by pressing the cup firmly against the sides and bottom.

For an extra clean and sharp look, I like to press the dough a little further up the sides past the top of the rim, and with a knife, scrape off the extra dough.

With a fork, prick the tart all over and bake for 10 minutes. Lower the heat to 350 degrees Fahrenheit, and bake for 7–10 minutes longer, until lightly golden. Place on a cooling rack and allow to cool while you make the filling.

Combine the avocado and sour cream in a food processor fitted with a metal blade, until well blended and completely smooth, about five minutes. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment, beat the cream cheese on medium speed until smooth, about three minutes. Add in the sugar and mix well. Then add the avocado mixture, flour and vanilla and mix until well combined.

Pour the filling into the cooled crust. Smooth the filling out with a spoon and chill until set. Decorate with fresh fruit and serve.