Preheat oven to 350°. Combine flour, sugar and salt in the bowl of a food processor. Roughly slice butter stick into 1/4" pieces and add to bowl. Pulse 5 or 6 times or until the butter is the size of small peas. Add egg and pulse a few more times until the egg is distributed. Place a piece of plastic wrap on the counter and dump mix onto it. Gather up edges and form dough into a disc, pressing the dough together with the plastic wrap.

Place dough in the center of an 11-inch tart shell and cover with the plastic wrap. Using the plastic wrap, push the dough into the shell and up the sides evenly. Use a small rolling pin or small dowel to make it evenly flat if you have one. Refrigerate until filling is made.

Prep plums by pitting and slicing them 1/4 inch thick. Set aside

Make filling. .If you use whole almonds, you will need to grind them in the food processor bowl with the sugar until fine. OR put the almond meal and sugar in the bowl.  Next add softened butter and process until it forms a ball in the bowl. Add eggs, vanilla, almond extract and flour. Process until all is combined.

Pour filling into tart shell. Top with overlying plum slices, peeling up. Place tart pan on a baking sheet and bake in 350° oven for 35-40 minutes or until filling is a golden brown color.