Mix all base ingredients together and press into an 8-inch pan, lined with parchment paper.
Using a hand mixer, whip filling ingredients to stiff peaks. Filling should be thick but still spreadable. If filling is too thick, whip in heavy cream 1 tbsp at a time until you reach desired texture. If desired, you can add the sweetener in smaller increments to taste.
Microwave topping ingredients together in 15-second increments until smooth. Spread evenly onto the base and filling.
Chill before serving.
Notes
If you have a hard time finding walnut or pecan meal, our recipe tester simply ground the pecans and walnuts into a flour using her blender.*Canadian style sour cream is thinner than American style. For a thinner, pudding-like texture, use 4 tablespoons American sour cream + 1/2 cup heavy cream.**Sweetener can be added in small increments to desired sweetness level.