Using a fork, smash together 2 oz. mild blue cheese, room temperature, and 4 Tbsp. unsalted butter, room temperature, in a small bowl.
Using a Microplane, finely grate in 1 garlic clove.
Add a small pinch of kosher salt and season with freshly ground pepper.
Blue cheese butter can be made 1 week ahead; cover, chill, and bring to room temp before using.
When ready to eat, spread blue cheese butter over 4 thick slices of bread, toasted.
Top with 2 large heirloom tomatoes, sliced; season with sea salt and more pepper.
Top with a scattering of coarsely chopped mixed tender herbs.
