Question

Which poetic technique does Robert Browning use in this excerpt from “My Last Duchess”? "Of joy into the Duchess' cheek: perhaps Frà Pandolf chanced to say "Her mantle laps Over my lady's wrist too much," or "Paint Must never hope to reproduce the faint Half-flush that dies along her throat:" such stuff Was courtesy, she thought, and cause enough For calling up that spot of joy. She had A heart—how shall I say?—too soon made glad," enjambment blank verse open form end-stopped lines

Answer 1

The poetic technique that Robert Browning used in his poem "My Last Duchess" is enjambment. 
That technique means that the thought found in one line of the poem does not end with the end of that line, but rather continues into the following line. There are no harsh endings of thought at the end of one line.

Answer 2

enjambment.  IS CORRECT