Grilled Cheese and Tomato Soup

1 yellow onion, finely chopped

2 garlic, minced

4 sandwich bread, thick slices

30 g unsalted butter, softened, divided

60 ml heavy cream

120 g cheddar cheese, grated

400 g crushed tomatoes, canned

250 ml vegetable stock

5 g granulated sugar

3 g kosher salt, to taste

1 g black pepper, freshly ground, to taste