In a medium bowl, stir peanut butter and butter together until smooth. Stir in the cocoa powder, sweetener, and vanilla extract until well combined.
Stir in the almond flour. The dough will become very stiff and hard to mix. Add water, 1 tbsp at a time, until you have a cohesive but stiff dough.
Press evenly into the bottom of a 9-inch springform pan. Top with a layer of waxed paper and smooth with a flat-bottomed glass or measuring cup. Refrigerate while preparing the ice cream.
No Churn Peanut Butter Ice Cream:
In a large bowl, beat together the sour cream, peanut butter, and 1/4 cup of the sweetener. In another large bowl, beat the whipping cream with the remaining 1/4 cup sweetener and the vanilla extract until stiff peaks form.
Gently fold whipping cream into peanut butter mixture until well combined and no streaks remain. Spread ice cream over brownie base and freeze until firm, 4 to 6 hours.
Before serving, drizzle with a little low carb chocolate sauce, if desired