Place the beets in a baking pan, drizzle with the oil, and season with salt. Cover with foil. Bake for about 1 hour, or until tender when pierced with a knife.
While the beets are roasting, make the dressing:
In a 1-quart non-reactive saucepan, over medium-high heat, reduce the tangerine juice to about 3/4 cup. Add the lemon juice. Remove from the heat and strain with a fine sieve.
Return to the saucepan; add lemon juice, salt and pepper. Over medium heat, reduce until the mixture bubbles and has a syrup-like consistency. You should have about 1/4 cup. Remove from the heat and strain again. Let cool to room temperature. Add the olive oil. Set aside. (Can be stored in refrigerator for up to 1 1/2 weeks.)
When cool enough to handle, peel the beets, and thinly slice them into rounds. Arrange on a serving platter and drizzle with the dressing. In a large bowl, toss the spinach with the remaining dressing and place spinach on top of beets in the center of the platter.
Remove the wedge of blue cheese from the freezer. Using a microplane grater, grate the desired amount over the salad. Garnish with toasted almonds.