Preheat oven to 375 degrees. Grease a 9” deep dish pie plate with butter and set aside.
Melt butter in a large skillet over medium high. When foaming subsides, add onion and sausage, season with salt and pepper, and saute, breaking up sausage with a spoon, until onion is translucent and sausage begins to brown, about 7 minutes.
Add kale and chicken stock or water and cook, stirring to deglaze the bottom of pan, until liquid is nearly evaporated kale is wilted, about 2 minutes. Remove from heat and let cool slightly.
In a large bowl, whisk to combine eggs and cream. Season lightly with salt and pepper and add thyme and reserved sausage mixture. Transfer to prepared pie plate. Distribute cheese and tomatoes over the top and transfer to oven. Bake until puffed and lightly golden, about 25-30 minutes.
Remove from oven and let cool slightly before cutting into pieces and serving.