Preheat oven to 350°F (175°C). Grease and line two 8-inch round cake pans.
In a medium bowl, whisk together the flour, baking powder, baking soda, and salt.
In a large bowl, cream the butter and sugar until light and fluffy. Add eggs one at a time, then stir in the vanilla extract and sourdough discard.
Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk. Mix until just combined.
Divide the batter evenly between the prepared pans. Bake for 35-40 minutes, or until a toothpick inserted into the center comes out clean. Let cool completely.
In a small saucepan, combine chopped strawberries, sugar, and lemon juice. Cook over medium heat for 10-15 minutes, mashing slightly, until thickened. Let cool completely.
In a chilled bowl, whip the heavy cream, powdered sugar, and vanilla extract until stiff peaks form.
Place one cake layer on a serving plate. Spread a layer of whipped cream, then pipe a border of whipped cream around the edge. Fill the center with the cooled strawberry jam.
Top with the second cake layer. Frost the top and sides (as you want) of the cake with the remaining whipped cream. Garnish with fresh strawberries if desired. Serve immediately or refrigerate.