Separate egg yolks from whites. Set aside whites for another use or discard. Push the yolks through a fine mesh strainer into a small bowl. Set aside.
***The benefit of using hard boiled egg yolks is to add the richness and flavor of the eggs without chemically changing the dough with the addition of raw egg yolks. This way the dough remains soft and light.
Combine flour, sugar, baking soda, cream of tartar, and salt in mixer bowl with a paddle attachment. Add butter pieces and mix on low until it resembles coarse meal.
Add yolks and cream. Mix until dough just comes together. Cover with a clean dish towel and set aside.
Preheat oven to 400*. Arrange apple and fig pieces in a 9x13" baking dish. They should be in a well-packed 2" layer. Dot with butter, sprinkle with sugar.
Bake, stirring every 3-5 minutes, for 10 minutes. Remove from oven as the apples just start to soften. Push fruit together into a mound to finish cooking. Cool to room temperature.
(These may be baked ahead of time and frozen up to 2 months, or refrigerated up to 3 days. Bring to room temp before using.)
After the fruit has cooled add walnuts. Stir to combine. Set aside.
Decrease oven temp to 375*. Prepare baking sheets by lining with parchment.
Roll out dough to 1/4" thickness. Cut into 3"x3" squares.
Add a generous tablespoon of the apple mixture to the center of each square. Brush edges with egg wash, fold over, pinch to seal. Place turnovers on baking sheets.
Brush turnovers with melted butter and sprinkle with sugar. (or wait to drizzle them with icing after they have cooled)
Bake 15-20 minutes, until light golden brown. Cool on wire rack.
These will keep 3 days in an airtight container or frozen up to 3 weeks.