1. Preheat oven to 325ºF. Butter a 9″inch round tart pan with a removable bottom.
2. In a mixer fitted with the paddle attachment cream butter, sugar and lemon zest until fluffy. Then add the flour and salt and mix until just combined. Divide the dough into two even pieces and wrap each in plastic wrap and chill in the fridge for one hour.
3. After dough has cooled, remove it from the fridge and place half the dough into the bottom of the tart pan. Press it down until it covers the bottom of the pan evenly and comes up the sides a little bit.
4. Roll out the almond paste with a rolling pin into a flat disk about 8″ round and place it on top of the bottom half of the dough. Then, place the remaining dough on top of the almond pasta and pat it down until it covers all of the almond paste and crimp the sides together to seal. Brush the egg wash lightly on top and scatter sliced almonds over it.
5.Bake for 35-40 minutes or until top is lightly golden and the edges are crispy and pulled away from the sides a little.
6. Allow to cool to room temperature and remove tart from the pan. Dust with confectioners’ sugar and serve.