In the bowl of a stand mixer, stir flour and yeast together until blended. Add water and mix well. It should be the consistency of thick cake batter. Cover the bowl with plastic wrap and let rise for 45 minutes, or until doubled. (If using active dry yeast, place the water in the bowl first, stir in yeast, and let stand until bubbly, about 5 minutes. Stir in flour.)
In a small bowl, stir fruit, rum, and vanilla extract together. Cover with a plate and let soak overnight. Measure almonds and chocolate and set the measuring cup on top of the plate (so you don’t forget about them!)
Measure flour and salt into a bowl, stir together, and set aside.
With the paddle attachment on medium speed, one at a time add eggs to the bowl of sponge, incorporating them after each addition. Mix in orange zest, sugar, and vanilla until combined.
On low speed, gradually add about 2 1/2 cups of flour. When incorporated, mix on medium-high speed for 3 minutes. The dough should be very soft and stretchy. On low speed, gradually add the remaining 1 1/2 cups of flour until incorporated.
Switch to the dough hook. Knead on low speed for 8 minutes, or until dough is very smooth and elastic. Stop two or three times to push dough that creeps up on the dough hook back into the bowl.
With the mixer on low speed, gradually add butter, a few slices at a time, until it is incorporated. Continue to mix with the dough hook for 3 minutes, until the dough is silky and shiny. If it still seems extremely sticky, gradually add from 1 to 2 tablespoons additional flour. The dough still should be very soft and sticky and will just barely pull away from the sides of the bowl, but not the bottom.
Pat the dough in the bowl into a ball. Spray lightly with vegetable oil spray and place a piece of plastic wrap directly on the surface of the dough. Refrigerate for 8 hours or up to 2 days.