4-8 oz Fresh Berries (recommend blackberries, raspberries, boysenberries. If you are more liberal with carbs, you can do pitted cherries or sliced plums)

.5 to 1 T Butter to butter pan

6 oz Greek Yogurt or Skyr (plain)

6 eggs

1/2 cup "Milk" (can be lactose free milk such as Fairlife, or almond or cashew milk, or for extra richness a combination of part cream/ part nut milk)

32 grams Casein + Whey Protein Powder (PEScience or Keto Chow recommended. I used PEScience White Chocolate Macadamia Nut, vanilla would also be great)

1 T Coconut Flour (add 1 more if you want it more cake-y than custardy)

30 g Sweetener (recommend Erythritol or Erythritol blend- allulose will taste fine but make the surface overly browned) - you can skip the sweetener if you don't think you need it as the protein powder is sweet.

1/2 tsp Vanilla extract

Either: 1 T Lemon Juice or 1/2 tsp Almond extract (depending on preferences - almond is more traditional, but I like lemon with berry!)

This could not be simpler.
Butter a 9" ceramic pie pan (can also make individual sized with ramekins, reduce cook time)
Wash and dry and lay out berries in pan.

Put all other ingredients in blender. Blend for 1 minute. Pour over berries. Batter should not go higher than 3/4 of pan as it will briefly puff up.

Bake 350 for 23-25 minutes. Let cool before serving. Should be served warm not hot.

If serving leftovers that have been stored in fridge, leave out for an hour or pop in microwave for 15 seconds to bring to room temperature.

I do big slices of this, though you can always serve smaller slices based on appetites.
Macros will vary depending on ingredients, but my version works out to 172 calories, 7.5 g fat, 7 g carbs, 19 g protein.