Make the Pound Cake: Preheat the oven to 350 degrees F. Butter a 6-cup loaf pan and line it with parchment or waxed paper.
In a small saucepan, bring the orange juice and saffron to a boil then turn the heat off immediately and let steep 5 minutes.
In a medium bowl, combine the flour, baking powder, and salt. In a mixer fitted with a whisk attachment (or using a hand mixer), cream the butter. Add 1 cup of the sugar and mix. With the mixer running at low speed, add the eggs one at a time. Working in alternating batches, and mixing after each addition, add the dry ingredients and 1/4 cup of the saffron spiked orange juice, trying to use all the threads in the orange juice. Mix just until smooth.
Pour into the prepared pan and bake until raised in the center and a tester inserted into the center comes out dry and almost clean (a few crumbs are OK), 65 to 75 minutes.
Meanwhile, make the glaze: In a small bowl, stir together the remaining 1/3 cup sugar and the remaining saffron spiked orange juice (about 1/3 cup), until the sugar is dissolved.
When the cake is done, let cool in the pan 15 minutes (it will still be warm). Run a knife around the sides of the pan. Set a wire rack on a sheet pan with sides (to catch the glaze) and turn the cake out onto the rack. Peel off the waxed paper. Using a turkey baster or pastry brush, spread glaze all over the top and sides of the cake and let soak in.
Repeat until all the glaze is used up, including any glaze that has dripped through onto the sheet pan. Let cool at room temperature or, wrapped in plastic wrap, in the refrigerator.
The cake will last up to a week, well-wrapped with plastic wrap.
Make the Lemon Caramel Sauce: Pour the sugar into the center of a deep saucepan. Carefully pour the water around the walls of the pan, trying not to splash any sugar onto the walls. Do not stir; gently draw your finger twice through the center of the sugar, making a cross, to moisten it. Over high heat, bring to a full boil and cook without stirring until amber-colored caramel, about 10 to 15 minutes, swirling the mixture occasionally to even out the color.
Add the lemon juice and vanilla and wait for the caramel to bubble and subside. Let the caramel cool.
To serve, cut the pound cake in thin slices and serve with scoops of cinnamon ice cream and a drizzling of lemon caramel sauce.