Whisk the ricotta, heavy cream, and the zest of 1/2 the lemon in a mixing bowl until combined. Add in the ¼ teaspoon of salt and a few cranks of black pepper. Taste the ricotta and adjust the seasoning as necessary.
Preheat the oven to 425°F. Lay the baguette slices out on a sheet pan and drizzle each with a little olive oil. Toast until they are golden brown, about 6 minutes.
Bring a large pot of water to a boil. Have a large mixing bowl ready with ice water. Blanch the kale for 1 to 2 minutes, until it is wilted.
Transfer the wilted kale to the ice water. When the kale is chilled, remove it from the ice water. As you remove the kale from the ice water, squeeze out all excess water. Take an extra minute on this step and really do a good job of squeezing out all the excess water from the kale. This will improve the taste and texture of your pesto. Transfer the kale to a food processor. Add the cheese, pine nuts, garlic, the juice of the lemon, and 1/2 cup of olive oil. Pulse in the food processor until it looks like pesto. Season with salt and freshly ground black pepper. Pulse. Taste. Adjust as necessary with more salt, pepper, and/or lemon juice.
Spread the ricotta mixture over the toasted baguette slices. Add a spoonful of the pesto to each crostini, then drizzle with olive oil, and season with freshly cracked black pepper and flaky sea salt.
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