Preheat oven to 300˚. Place 2 cups flour, 1/2 cup sugar, the butter, and any additional lemon zest in food processor that has been fitted with the blade attachment. Pulse until mixture resembles fine crumbs.
With food processor running, add 2 egg yolks through the chute. Continue processing until dough has balled up on one side of the bowl, about 1-2 minutes.
Press dough firmly into bottom of 11" tart pan, pressing up the sides. If you have a small rolling pin you can use that to smooth the bottom and finish the edges.
Line with aluminum foil and fill with pie weights or poke bottom with fork to prevent puffing up during initial baking.
Bake for 20-30 minutes. Transfer to wire rack and cool completely before filling and baking a second time.
Preheat oven to 325˚. Beat 3 eggs at high speed until foamy. Gradually add 1 cup sugar, mixture will be thicker and lighter.
Add 1 Tablespoon lemon zest, remaining 1/4 cup flour, baking powder and 1/3-1/2 cup lemon juice. Beat slowly for 30 seconds to combine, then turn up to high speed for 30-60 seconds to mix well.
Pour filling into tart shell. (You will likely have more filling than will fit.)
Bake for 20-25 minutes until filling is set and top is just beginning to brown at the edges. Transfer to wire rack and cool completely.
Puree raspberries in food processor or blender until smooth. Pour into mesh sieve or metal strainer that is fit over a medium bowl. Push sauce through strainer with rubber spatula leaving seeds in the strainer. (One or two may make there way into the sauce and that is ok.)
Whisk about 1/4 cup sugar into pureed raspberries. The amount of sugar will vary with the sweetness of the berries, so you may need a little more or less. Serve immediately or store in a tightly sealed container in the fridge. The sauce keeps well for several days.
Dust tart with powdered sugar, garnish with lemon slices (optional). Serve with a drizzle of raspberry sauce.
Enjoy!