Grease an 8x8" baking dish, fill with sliced croissants and mixed berries. Set aside.
Add cream cheese to mixing bowl and beat with hand mixer until smooth. Add milk, sugar, eggs, vanilla and lemon zest and beat until combined.
Pour mixture over croissants and berries.
Cover with plastic wrap and refrigerate overnight.
Remove baking dish from refrigerator and let sit on the counter.
Preheat oven to 350 degrees F.
Bake, covered with aluminum foil, for 30 minutes. Remove foil and bake uncovered for 15 minutes, until golden and when a knife inserted in center comes out clean.
While casserole is baking, add powdered sugar, heavy cream, and vanilla bean paste to a small mixing bowl and whisk to combine until smooth and pourable.
Drizzle glaze over croissant puff after it's finished baking. Serve warm.
Notes
You can bake this dish the same day you make it, if needed. Just be sure to let the croissant puff sit for 10 minutes or so before baking so the croissants can soak up some of the liquid.