The tangy taste of citrus is especially welcome in winter!
In a food processor, pulse almonds, granulated sugar, and 1/2 teaspoon salt until finely ground. Add flour; pulse to combine. Add butter and pulse until mixture is crumbly and holds together when squeezed. Press crumbs in bottom and up side of an 8-inch fluted tart pan with a removable bottom. Freeze 15 minutes. (To store, cover and freeze, up to 1 month.)
Preheat oven to 350 degrees. Place tart pan on a rimmed baking sheet and bake until crust is golden brown and set, 30 to 35 minutes. Let cool on a wire rack 10 minutes, then remove tart ring and let cool completely.
In a small bowl, sprinkle gelatin over 2 tablespoons cold water and let stand 5 minutes. In a small saucepan, warm half-and-half over medium. When it begins to steam, add gelatin mixture and stir until dissolved, about 1 minute. In a medium bowl, whisk together yogurt, brown sugar, and pinch of salt. Stir warm half-and-half mixture into yogurt mixture. Pour filling into cooled tart shell and refrigerate until set, 2 hours (or up to 1 day).
With a sharp paring knife, slice off ends of oranges. Following curve of fruit, cut away peel, removing as much white pith as possible. Slice oranges into 1/4-inch-thick rounds and remove any seeds. Just before serving, arrange orange slices on top of tart.
If you'd like, save the orange peels to make Candied Citrus Peel. Cut off the outermost peel of the fruit and reserve, then cut off remaining pith and discard.