How to transpose only some columns to rows from a dataframe in R?

Question

I have a dataframe that looks like this:

df1 <- data.frame(class = c(1,2,3,4,5),
                 value = c(1,2,2,3,3),
                 spec =  c("A", "B","C", "D", "E"))

I want to transpose it as such that class becomes headers of columns, spec remains a column and values become rows, so it wood look like this:

spec 1 2 3 4 5
A    1
B      2
C        2
D          3
E            3