Combine sliced strawberries, sugar, and lemon juice in a large bowl. Toss to combine. Let sit for 1–2 hours to release their juices.
Preheat oven to 425°F.
Combine the cake flour, salt, baking powder, cream of tartar, and sugar in a large bowl.
Cut butter into small bits and add to the dry ingredients. Using a pastry cutter or fork, work butter in until the mixture resembles coarse breadcrumbs.
Add the beaten egg and heavy cream and mix with a fork until the mixture just holds together.
Turn out onto a well-floured surface and knead by folding over 8–10 times, rotating as you go.
Pat into a ½-inch thick rectangle. Cut into 6 larger or 8 smaller equal squares.
Place biscuits on a parchment-lined baking sheet (do not grease). Separate biscuits slightly for crispier edges, or place touching for softer sides.
Bake 15–20 minutes until light golden brown.
While the shortcakes bake, add the heavy cream, powdered sugar, and vanilla extract to a clean bowl. Whip with a hand or stand mixer until soft peaks form.
Slice shortcakes in half horizontally. Spoon a generous helping of macerated strawberries onto the bottom half, top with a dollop of homemade whipped cream, place the top half on, and serve immediately. Enjoy!