For the Strawberry Rhubarb Shortcake:

1. Add cubed butter to the freezer to chill for 10 minutes before making your biscuits.
2. Add quartered strawberries, ¼ cup of sugar, and a small pinch of salt to a large bowl and mix to combine. Set aside for 1 hour while you prep the rest of your ingredients to let the juices release from the strawberries. 
3. Meanwhile, make the biscuits. In a large bowl, add the flour, sugar, baking powder, baking soda, salt, and orange zest and whisk to combine. Add the cold butter and work it into the flour using a pastry cutter or your fingers until you see mostly pea sized pieces, with a few slightly larger chunks (this creates flakiness!)
4. Pour in the cold buttermilk and vanilla and gently mix with a fork until a shaggy dough forms. You want to work the dough as little as possible, so you get a crumbly flaky texture vs tough. It should look a little dry and messy – this is good, as working the dough as little as possible results in the flakiest layers. Place in the fridge for 10 minutes to chill.
5. Turn dough onto a lightly floured surface and using a floured rolling pin or your hands, roll into a 1” thick rough rectangle. Using a knife or bench scraper, cut the dough into 4 square pieces. Stack each piece of dough on top of each other, pressing in any loose bits of dough between the layers. Roll into a rectangle again, then repeat the stacking process one more time. Roll the dough into a 1” thick rectangle. 
6. Using a biscuit cutter or glass, press down to cut dough into ~3” round biscuits. Do not twist the dough cutter, just lift straight up. Twisting seals the edges which prevents rising.
7. Transfer the biscuits to a parchment paper lined baking sheet and freeze for 10-15 minutes while the oven preheats.
8. Preheat the oven to 425°F.
9. While the biscuits are chilling, make the strawberry rhubarb filling. To a saucepan, add the rhubarb, sugar, orange zest, vanilla, and salt. Strain the juices from the macerated strawberries into the pan and set the strawberries aside for later.
10. Bring the rhubarb mixture to a gentle boil, then stir and reduce to simmer for 5-7 minutes or until soft but not mushy. Shut off the heat and let cool slightly, before folding into the bowl of strawberries. 
11. Bake your biscuits. Brush the tops with buttermilk or heavy cream and sprinkle with coarse sugar and flaky sea salt. 
12. Bake at 425°F for 18-22 minutes or until the tops are golden brown and the edges are crisp. Let cool for 10 minutes before slicing. 
13. While the shortcakes are baking, make the mascarpone whipped cream. To a bowl with a stand mixer (or regular bowl with an electric whisk), add the mascarpone, heavy cream, sugar, and vanilla bean extract. Whip on high until soft peaks form, usually 2-3 minutes. You do not want to overwhip, as it can result in the cream being grainy. If you accidentally overwhipped, just fold in a bit more heavy cream. Place in the fridge until ready to use.
14. To assemble your shortcakes, halve the shortcakes lengthwise. Top with a hefty dollop of the mascarpone whipped cream, then the strawberry rhubarb mixture, then top with the other half of the shortcake. Serve immediately!