Step 1

Whisk 1 (3.4-ounce) box instant lemon pudding mix, 3/4 cup of the cold heavy cream, and 3 tablespoons lemon juice together in a large bowl until smooth. Let sit until thickened, about 5 minutes.

Step 2

Meanwhile, beat the remaining 1 cup cold heavy cream, 2 tablespoons powdered sugar, and 1/4 teaspoon kosher salt together in a stand mixer with the whisk attachment on medium speed until soft peaks form, 3 to 4 minutes. Add 1/2 cup marshmallow crème and beat on medium speed until stiff peaks form, 1 to 2 minutes.

Step 3

Add the marshmallow mixture and 1 1/2 cups coarsely crushed shortbread cookies to the pudding and fold together with a flexible spatula until just combined.

Step 4

Divide between 4 serving cups. Garnish with more crushed shortbread cookies and lemon zest if desired.