Preheat oven to 450°F. Place 2 tablespoon butter in 12" cast iron skillet and put the skillet in the oven.
While skillet is heating up, add remaining 2 tablespoon melted butter, eggs, milk, flour, ricotta, sugar, vanilla extract, salt and lemon zest to blender and blend on high for 1 minute or until batter is smooth. Remove skillet from oven and pour batter in. Sprinkle raspberries on top of batter.
Bake for 20 minutes and then reduce temperature to 300°F and bake for another 5 minutes. DO NOT open oven during the first 15 minutes or the pancake might deflate. Remove when pancake is puffed and brown on top. Top with whipped ricotta, fresh raspberries and maple syrup.
Whipped Ricotta Cream
In bowl of stand mixer with whisk attachment, whip the ricotta and cream until smooth and fluffy, about 5 minutes. Add maple syrup and vanilla extract and whip until combined.
Room Temperature Ingredients: If time permits, make sure the butter, eggs and milk are room temperature.
Mix Well: It's important to make sure all of the ingredients are mixed well, which is why a blender works great. But you can go old school and just use a wooden spoon to mix everything.
Preheat the Skillet: It's important to preheat the skillet so it's ready as soon as the batter hits the pan. This contributes to the browning on the bottom of the pancake and its rise. If you have time, let the skillet sit in a heated up oven for at least 30 minutes before adding butter, then the batter.
Use Cast Iron: Cast iron skillets are meant for dutch babies. If you don't have a cast iron skillet, make sure you are using a pan that can go in the oven.
Make Batter Ahead of Time: If you want a really tall pancake, make the batter ahead of time and place in airtight container in the fridge overnight. You can actually keep batter for the lemon Dutch baby in fridge for up to 3 days before using it.